Hyperspectral optical analysis of Zumpango Lake, Mexico
Análisis óptico hiperespectral del Lago de Zumpango, México
Raúl Aguirre Gómez
* Laboratorio de Análisis Geoespacial (lage), Instituto de Geografía, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica, Ciudad Universitaria, 04510, Coyoacán, México, D. F.
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class="elsevierStyleSimplePara elsevierViewall">Mapa de formas del relieve.</p>" ] ] ] "autores" => array:1 [ 0 => array:2 [ "autoresLista" => "Gabriel Legorreta Paulín, José Lugo Hubp" "autores" => array:2 [ 0 => array:2 [ "nombre" => "Gabriel Legorreta" "apellidos" => "Paulín" ] 1 => array:2 [ "nombre" => "José Lugo" "apellidos" => "Hubp" ] ] ] ] ] "idiomaDefecto" => "es" "EPUB" => "https://multimedia.elsevier.es/PublicationsMultimediaV1/item/epub/S018846111470888X?idApp=UINPBA00004N" "url" => "/01884611/0000201400000084/v2_201506250143/S018846111470888X/v2_201506250143/es/main.assets" ] "en" => array:18 [ "idiomaDefecto" => true "titulo" => "Hyperspectral optical analysis of Zumpango Lake, Mexico" "tieneTextoCompleto" => true "paginas" => array:1 [ 0 => array:2 [ "paginaInicial" => "32" "paginaFinal" => "41" ] ] "autores" => array:1 [ 0 => array:3 [ "autoresLista" => "Raúl Aguirre Gómez" "autores" => array:1 [ 0 => array:4 [ "nombre" => "Raúl Aguirre" "apellidos" => "Gómez" "email" 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F." "etiqueta" => "*" "identificador" => "aff0005" ] ] ] ] "titulosAlternativos" => array:1 [ "es" => array:1 [ "titulo" => "Análisis óptico hiperespectral del Lago de Zumpango, México" ] ] "resumenGrafico" => array:2 [ "original" => 0 "multimedia" => array:7 [ "identificador" => "f0015" "etiqueta" => "Figure 3" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr3.jpeg" "Alto" => 945 "Ancho" => 1300 "Tamanyo" => 67427 ] ] "descripcion" => array:1 [ "en" => "<p id="sp0015" class="elsevierStyleSimplePara elsevierViewall">Typical derivative reflectance spectrum of Zumpango Lake.</p>" ] ] ] "textoCompleto" => "<span class="elsevierStyleSections"><span id="sec0005" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0025"><a name="p33"></a>Introduction</span><p id="par0005" class="elsevierStylePara elsevierViewall">The Basin of Mexico is a highland surrounded by volcanic mountains. It is at the central-eastern part of the Trans-Mexican Volcanic Belt, located between 98°15’ and 99°30’ W, and 19°<span class="elsevierStyleHsp" style=""></span>00’ and 20°<span class="elsevierStyleHsp" style=""></span>15’ N. Altitude varies from 2240<span class="elsevierStyleHsp" style=""></span>m<span class="elsevierStyleHsp" style=""></span><span class="elsevierStyleSmallCaps">asl</span> to the south to 2390<span class="elsevierStyleHsp" style=""></span>m<span class="elsevierStyleHsp" style=""></span><span class="elsevierStyleSmallCaps">asl</span> to the north. This basin is endorheic, or hydrologically closed, and has an approximate area of 9600<span class="elsevierStyleHsp" style=""></span>km<span class="elsevierStyleSup">2</span><span class="elsevierStyleHsp" style=""></span>and includes parts of the Federal District, and the States of Mexico, Hidalgo, Tlaxcala and Puebla.</p><p id="par0010" class="elsevierStylePara elsevierViewall">Its present morphological features were established during the quaternary period; tectonic and volcanic activities continue nowadays.</p><p id="par0015" class="elsevierStylePara elsevierViewall">Formerly, there were lacustrine flatlands, occupying the lower part of the area. This basin contained five lakes: Zumpango, Xaltocan, and Texcoco of brackish water, to the north, and, to the south Xochimilco and Chalco of fresh water, at the western side and at a higher altitude than the other three (Gutiérrez de <a class="elsevierStyleCrossRef" href="#bib0065">MacGregor, 1995</a>; <a class="elsevierStyleCrossRef" href="#bib0100">Lugo <span class="elsevierStyleItalic">et al</span>., 2001</a>).</p><p id="par0020" class="elsevierStylePara elsevierViewall">However, the morphology of the lacustrine flatland has changed as a result of anthropogenic modifications made since historical times. All the lakes have virtually disappeared, leaving just a few relicts. The most important relicts are Tecocomulco and Zumpango lakes and the Guadalupe dam, all at the northern side of the basin. In the southern part, there are no water bodies of a significant size, even though some relicts do remain in the form of channels of the ancient Xochimilco Lake.</p><p id="par0025" class="elsevierStylePara elsevierViewall">There are a number of studies performed in Mexican lakes using remote sensing techniques (e. g. <a class="elsevierStyleCrossRef" href="#bib0030">Chacón <span class="elsevierStyleItalic">et al</span>., 1992</a>; <a class="elsevierStyleCrossRef" href="#bib0115">Mendoza <span class="elsevierStyleItalic">et al</span>., 2007</a>). In particular, in the Basin of Mexico, <a class="elsevierStyleCrossRef" href="#bib0150">Prol-Ledesma <span class="elsevierStyleItalic">et al</span>. (2002)</a> used satellite imagery to analyze the neighborhood of Lake of Chalco; De la <a class="elsevierStyleCrossRef" href="#bib0045">Lanza and Gómez (2005)</a> performed a change detection study in the vicinity of Tecocomulco Lake.</p><p id="par0030" class="elsevierStylePara elsevierViewall">Nowadays, it is possible to accurately assess the trophic conditions of a water body by using hyperspectral remote sensors to measure in situ reflectance. To validate this information, fieldwork must calibrate remote sensing data by in situ measurement of photosynthetic pigment concentration in the water body such as chlorophyll a, b, c, and carotenoids (<a class="elsevierStyleCrossRef" href="#bib0055">Glooschenko <span class="elsevierStyleItalic">et al</span>., 1974</a>; <a class="elsevierStyleCrossRef" href="#bib0010">Brivio <span class="elsevierStyleItalic">et al</span>., 2001</a>; <a class="elsevierStyleCrossRef" href="#bib0005">Aguirre <span class="elsevierStyleItalic">et al</span>., 2001</a>). One of the main advantages of this kind of study is the possibility of using sophisticated mathematical functions to perform a deeper analysis than that used with broad band satellite data. Thus, the aim of this paper is to analyze the spectral response of Zumpango Lake by using a hyperspectral remote sensor.</p></span><span id="sec0010" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0030">Study area</span><p id="par0035" class="elsevierStylePara elsevierViewall">Zumpango Lake is in the north-eastern region of the State of Mexico located at 19°<span class="elsevierStyleHsp" style=""></span>46’ N and 99°<span class="elsevierStyleHsp" style=""></span>9’ W (<a class="elsevierStyleCrossRef" href="#f0005">Figure 1</a>). Topographically, the lake is characterized by flatlands to the south, although the north-eastern end is rather hilly with altitudes varying between 1 245 and 1 650<span class="elsevierStyleHsp" style=""></span>m <span class="elsevierStyleSmallCaps">asl</span>.</p><elsevierMultimedia ident="f0005"></elsevierMultimedia><p id="par0040" class="elsevierStylePara elsevierViewall">The lake is part of the Moctezuma river hydro-logical basin (<a class="elsevierStyleCrossRef" href="#bib0075"><span class="elsevierStyleSmallCaps">inegi</span>, 1998</a>). It is fed by runoff from the nearby mountain slopes that is not absorbed by, nor filtered through, the soil.</p><p id="par0045" class="elsevierStylePara elsevierViewall">The lake has a maximum extension of 24<span class="elsevierStyleHsp" style=""></span>km<span class="elsevierStyleSup">2</span><span class="elsevierStyleHsp" style=""></span>and a depth between 1-3<span class="elsevierStyleHsp" style=""></span>m, although both vary seasonally and annually as a function of precipitation. Yearly total precipitation averages 700<span class="elsevierStyleHsp" style=""></span>mm, reaching a maximum in June. The climate is cold from November to March, with temperatures down to -2.3°<span class="elsevierStyleHsp" style=""></span>C, and warm from April to October with temperatures up to 31°C; the annual mean is 15°<span class="elsevierStyleHsp" style=""></span>C (<a class="elsevierStyleCrossRef" href="#bib0080"><span class="elsevierStyleSmallCaps">inegi</span>, 2005</a>).</p><p id="par0050" class="elsevierStylePara elsevierViewall">The lake also works as a controlling and storage basin with a capacity for 100<span class="elsevierStyleHsp" style=""></span>million<span class="elsevierStyleHsp" style=""></span>cubic meters; over 60<span class="elsevierStyleHsp" style=""></span>million<span class="elsevierStyleHsp" style=""></span>cubic meters of water per year regularly enter. Recently, Zumpango Lake has been undergoing a constant rescue operation (<a class="elsevierStyleCrossRef" href="#bib0070">H. Ayuntamiento del Estado de México, 2003</a>). In January 2003 the lake was promoted to “water sanctuary” and in order to keep this status there is frequent cleaning work, which consists mainly of smashing mats of aquatic hyacinth (<span class="elsevierStyleItalic">Eichhornia sp</span>) a very prolific and abundant species with a seasonal growth pattern (<a class="elsevierStyleCrossRef" href="#bib0155">` <span class="elsevierStyleItalic">et al</span>., 2005</a>). Hyacinth smashing causes a homogeneous greenish color of the water body.<a name="p34"></a></p></span><span id="sec0015" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0035">Methods and material</span><p id="par0055" class="elsevierStylePara elsevierViewall">Fieldwork was carried out at Zumpango Lake on August 2006. Seven sampling points were selected. Six of them (1-5, 7) were distributed surrounding the lake for covering the input of water in it and the last one <a class="elsevierStyleCrossRef" href="#fq0030">(6)</a> was located at the deepest zone of the lake, close to the centre of the water body. Each sampling point was geo-referred with a <span class="elsevierStyleSmallCaps">gps</span> (Garmin, Ltd) and optical measurements such as Secchi transparency and hyperspectral reflectance were also performed. Afterwards, hyperspectral data were analyzed through a derivative method. Water samples were collected at each sampling site at the surface and at 0.5<span class="elsevierStyleHsp" style=""></span>m<span class="elsevierStyleHsp" style=""></span>depth for laboratory analysis of chlorophyll concentration using fluorometric methods.</p><span id="sec0020" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0040">Secchi transparency and extinction coefficient k</span><p id="par0060" class="elsevierStylePara elsevierViewall">Transparency was measured with a Secchi disk. It is a white, heavy disk, with a diameter of about 30 centimeters. The disk is submerged into the water body until it is no longer visible, as observed from the sunny side of the boat avoiding the shadow (<a class="elsevierStyleCrossRef" href="#bib0035">Davies-Colley <span class="elsevierStyleItalic">et al</span>., 1993</a>). This measurement allows for an acceptable estimated of the light extinction coefficient. <a class="elsevierStyleCrossRef" href="#bib0185">Tyler (1968)</a> found a 15% variation between measurements taken with this simple instrument and submerged photometers. Transparency measured with a Secchi disk is, basically, a function of light reflected by the disk surface, and hence it is affected by absorption characteristics of the water and the elements contained within it. The higher the dissolved or suspended <a name="p35"></a>organic matter concentration the lower the transparency, due to absorption and scattering processes (<a class="elsevierStyleCrossRef" href="#bib0145">Preisendorfer, 1986</a>). On the one hand, there is an exponential decrement due to yellow substance and, on the other hand, there is a reduction of the transparency due to the increment of scattered light by suspended particulate matter, as pointed out by <a class="elsevierStyleCrossRef" href="#bib0200">Wetzel (1975)</a>. Calculation of the extinction coefficient (K) was theoretically proposed by <a class="elsevierStyleCrossRef" href="#bib0175">Sverdrup <span class="elsevierStyleItalic">et al.</span> (1942)</a>, and empirically adjusted by <a class="elsevierStyleCrossRef" href="#bib0105">Margalef (1983)</a>. The empirical relationship has been expressed as follows:</p><p id="par0065" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="fq0005"></elsevierMultimedia></p><p id="par0070" class="elsevierStylePara elsevierViewall">where 0.03 is the water extinction value at 540<span class="elsevierStyleHsp" style=""></span>nm; 0.0015 is the extinction due to chlorophyll <span class="elsevierStyleItalic">a</span> in<span class="elsevierStyleHsp" style=""></span>mg<span class="elsevierStyleHsp" style=""></span>m<span class="elsevierStyleSup">-3</span>; ∑i34Vidi is the extinction due to suspended particles and D is the depth observed with the Secchi disk.</p><p id="par0075" class="elsevierStylePara elsevierViewall"><a class="elsevierStyleCrossRef" href="#bib0175">Originally, Sverdrup <span class="elsevierStyleItalic">et al</span>. (1942)</a> proposed a constant of 2.3, obeying the exponential characteristic of pure water absorption. However, Margalef’s adjustment takes into account the actual elements in the water volume. Thus, empirically, a constant of 1.7 is the value best adjusted to experimental data obtained in a number of different water bodies.</p></span><span id="sec0025" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0045">Hyperspectral measurements</span><p id="par0080" class="elsevierStylePara elsevierViewall">Reflectance data were recorded at each sampling point with a hyperspectral spectroradiometer (<span class="elsevierStyleSmallCaps">ger</span>-1500). This radiometer is portable and gives fast hyperspectral scanning; it has a spectral range from 380<span class="elsevierStyleHsp" style=""></span>nm to 1100<span class="elsevierStyleHsp" style=""></span>nm. It has an objective lens with 8°<span class="elsevierStyleHsp" style=""></span>field of view that allows for a precise focusing on the target. However, optical radiation measurements are carried out through an aperture with a field of view of only 1º. <span class="elsevierStyleSmallCaps">ger</span>-1500 has a spectral precision of<span class="elsevierStyleHsp" style=""></span>±<span class="elsevierStyleHsp" style=""></span>2<span class="elsevierStyleHsp" style=""></span>nm. The instrument also has an integrating card of 512K containing the <span class="elsevierStyleSmallCaps">ger</span>-1500 operating program, correcting factors and memory slots for up to 400 readings. These measurements can be handled as output <span class="elsevierStyleSmallCaps">ascii</span> files.</p><p id="par0085" class="elsevierStylePara elsevierViewall">Reflectance was measured by the Bi-Directional Reflectance Factor (<span class="elsevierStyleSmallCaps">brf</span>) method derived from the Bi-Directional Reflectance Distribution Function (<span class="elsevierStyleSmallCaps">bdrf</span>) proposed by <a class="elsevierStyleCrossRef" href="#bib0180">Swain and Davis (1978)</a> and by <a class="elsevierStyleCrossRef" href="#bib0120">Milton (1987)</a>. The <span class="elsevierStyleSmallCaps">brf</span> method is based on the use of a perfect reflecting and diffusing surface as a reference. Thus, the reflectance factor is defined as the ratio between the reflected flux from a target under specific irradiance and observation conditions and the diffusing surface identically irradiated and observed. Perfect diffusion means that the surface isotropically reflects radiation; such surfaces are known as “lambertians”. Since natural targets are not perfectly diffusing surfaces, intensity of reflected flux depends on the outgoing flux angle. Perfect reflection means that the entire flux incident on the surface is reflected from it, and neither absorption nor transmitting processes are involved. Since in practice, there are no such panels or surfaces with these properties, a correction must be applied considering the spectral reflectance from the panel. Hence, <span class="elsevierStyleSmallCaps">brf</span> is defined as follows:</p><p id="par0090" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="fq0010"></elsevierMultimedia></p><p id="par0095" class="elsevierStylePara elsevierViewall">where dL<span class="elsevierStyleInf"><span class="elsevierStyleInf">t</span></span> is the target radiance, dL<span class="elsevierStyleInf"><span class="elsevierStyleInf">p</span></span> is the reference radiance under the same specific illumination and observation conditions, and <span class="elsevierStyleItalic">k</span> is the panel correction factor. Incoming and outgoing radiation were sequentially measured three times and afterwards averaged. Outgoing radiation was measured by pointing the sensor at the sunny side of the boat in order to avoid its shadow, which can produce an error of up to 30% (<a class="elsevierStyleCrossRef" href="#bib0060">Gordon, 1985</a>). The sensor was positioned to obtain a nadir view of the water surface. This setting reduces unwanted radiances from the reflected light that is independent from the optical properties of water (<a class="elsevierStyleCrossRef" href="#bib0170">Shifrin, 1988</a>). Incoming radiation was measured by observing a halon reference panel (polytetrafluoretylene). It is a resistant and hydrophobic panel (i. e. washable and insensitive to humidity changes), so is suitable for fieldwork (<a class="elsevierStyleCrossRef" href="#bib0195">Weidner and Hsia, 1981</a>; <a class="elsevierStyleCrossRef" href="#bib0165">Schutt <span class="elsevierStyleItalic">et al</span>., 1981</a>).</p><p id="par0100" class="elsevierStylePara elsevierViewall">Reflectance spectra were obtained by measuring water body radiance and then sequentially measuring the halon panel radiance. The ratio of <a name="p36"></a>the two measurements was applied as stated in <a class="elsevierStyleCrossRef" href="#fq0010">equation 2</a> and multiplied by a correction factor of 0.99 according to the manufacturer’s manual. Reflectance spectra were corrected for water/sky glint by subtracting the reflectance measured at 750<span class="elsevierStyleHsp" style=""></span>nm from each spectrum. It is assumed that at this wavelength water absorbs all the incoming radiation. Care must be taken at the blue end of the electromagnetic spectrum since imprecision due to scattering may occur.</p></span><span id="sec0030" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0050">Derivative analysis</span><p id="par0105" class="elsevierStylePara elsevierViewall">To obtain fourth-order derivative spectral curves, a homemade algorithm was written in Matlab, which includes a 15-point convolution filter based on Savitzky and <a class="elsevierStyleCrossRef" href="#bib0160">Golay’s coefficients (1964)</a>, expressed as follows:</p><p id="par0110" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="fq0015"></elsevierMultimedia></p><p id="par0115" class="elsevierStylePara elsevierViewall">with a normalization factor N<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>92378. <a class="elsevierStyleCrossRef" href="#fq0015">Equation 3</a> was applied to the original reflectance curves measured in the field.</p><p id="par0120" class="elsevierStylePara elsevierViewall">This type of filter is routinely used on conventional <span class="elsevierStyleSmallCaps">uv</span>-<span class="elsevierStyleSmallCaps">vis-ir</span> spectrophotometers.</p><p id="par0125" class="elsevierStylePara elsevierViewall">Maxima found in the spectral derivatives correspond to reflectance peaks while minima are associated with absorption peaks (<a class="elsevierStyleCrossRef" href="#bib0005">Aguirre <span class="elsevierStyleItalic">et al</span>., 2001</a>).</p></span><span id="sec0035" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0055">Phytoplankton data</span><p id="par0130" class="elsevierStylePara elsevierViewall">Phytoplankton samples were collected at the seven sampling points using plastic bottles at the surface and at the Secchi depth for later quantitative analysis. Samples were frozen for subsequent laboratory analysis. Concentrations of chlorophyll <span class="elsevierStyleItalic">a</span> (Chl <span class="elsevierStyleItalic">a</span>) at selected stations were obtained from a 200<span class="elsevierStyleHsp" style=""></span>ml sample of surface water and were extracted with acetone at 90% and then filtered through 0.45<span class="elsevierStyleHsp" style=""></span>µm<span class="elsevierStyleHsp" style=""></span>glass-fiber filters (Whatman GF/F) ground and centrifuged. Fluorometric measurement of Chl <span class="elsevierStyleItalic">a</span> was performed by the method of <a class="elsevierStyleCrossRef" href="#bib0085">Holm-Hansen <span class="elsevierStyleItalic">et al</span>. (1965)</a> using a Sequoia-Turner Model 450 fluorometer (Sequoia-Turner Corporation, MountainView,<span class="elsevierStyleSmallCaps">ca</span>,<span class="elsevierStyleSmallCaps">usa</span>) with excitation filter at 440<span class="elsevierStyleHsp" style=""></span>nm and emission filter at 665<span class="elsevierStyleHsp" style=""></span>nm as described by <a class="elsevierStyleCrossRef" href="#bib0130">Parsons <span class="elsevierStyleItalic">et al</span>. (1984)</a>. Standard Chl <span class="elsevierStyleItalic">a</span> calibration for determination was performed by the method described by <a class="elsevierStyleCrossRef" href="#bib0190"><span class="elsevierStyleSmallCaps">unesco</span> (1994)</a>. Chl <span class="elsevierStyleItalic">a</span> reagent (Wako Pure Co. Ltd., super grade) was dissolved in 90% acetone. The specific absorption coefficient is 87.67 for 90% acetone (<a class="elsevierStyleCrossRef" href="#bib0090">Jeffrey and Humphrey, 1975</a>; <a class="elsevierStyleCrossRef" href="#bib0140">Porra <span class="elsevierStyleItalic">et al</span>., 1989</a>). Using these precise Chl <span class="elsevierStyleItalic">a</span> concentrations, a factor (ti) of the equation for fluorometric Chl <span class="elsevierStyleItalic">a</span> determination was calculated for 90% acetone:</p><p id="par0135" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="fq0020"></elsevierMultimedia></p><p id="par0140" class="elsevierStylePara elsevierViewall">where [Chl <span class="elsevierStyleItalic">a</span>] is in µgl<span class="elsevierStyleSup">-1</span>; Fo is the original fluorescence, Fa is the fluorescence after acidification, and v is the dilution factor from the volume of filtered and extracted solution. In this study, all Chl <span class="elsevierStyleItalic">a</span> determinations were performed in duplicate.</p></span></span><span id="sec0040" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0060">Trophic state index</span><p id="par0145" class="elsevierStylePara elsevierViewall">In order to relate [Chl <span class="elsevierStyleItalic">a</span>] to Secchi transparency a comparative analysis between the two variables was carried out. The trophic state can be defined as the total weight of living biological material (<span class="elsevierStyleItalic">biomass</span>) in a water body at a specific location and time. According to this definition, <a class="elsevierStyleCrossRef" href="#bib0015">Carlson (1977)</a> proposed a trophic state index (<span class="elsevierStyleSmallCaps">tsi</span>) using algal biomass as the basis for trophic state classification. In this he included three variables: chlorophyll pigments, Secchi depth, and total phosphorus. The index reflects a continuum of “states.” Thus, the trophic continuum is divided into units based on a base-2 logarithmic transformation of Secchi depth. The range of the index is from approximately 0 to 100, although the index has theoretically no lower or upper bounds. The logarithmic transformation of the data normalizes the skewed data distribution, allowing the use of parametric statistics such as mean, standard deviation, parametric comparison tests.</p><p id="par0150" class="elsevierStylePara elsevierViewall">The three index variables are interrelated by linear regression models, and should produce the same index value for a given combination of variable values. Thus, any of the three variables can theoretically be used to classify a water body. In this paper we only included Secchi disk transparency (SD) and Chlorophyll <span class="elsevierStyleItalic">a</span> concentration (Chl <span class="elsevierStyleItalic">a</span>) values, since total phosphorus analysis were not <a name="p37"></a>performed. For the purpose of classification, priority is given to chlorophyll, because this variable is the most accurate of the three at predicting algal biomass. The Trophic State Index (<span class="elsevierStyleSmallCaps">tsi</span>) was calculated by using a couple of simplified equations:</p><p id="par0155" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="fq0025"></elsevierMultimedia></p><p id="par0160" class="elsevierStylePara elsevierViewall"><elsevierMultimedia ident="fq0030"></elsevierMultimedia></p></span><span id="sec0045" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0065">Results and analysis</span><p id="par0165" class="elsevierStylePara elsevierViewall">Reflectance curves are the resulting combination of spectral signatures from phytoplankton and aquatic vegetation, mainly at the green and infrared regions. The reflective responses of the seven sampling points in Zumpango Lake were alike, having a similar shape but a slightly different magnitude (<a class="elsevierStyleCrossRef" href="#f0010">Figure 2</a>). Hence, derivative reflectance spectrum from each sampling site was analogous.</p><elsevierMultimedia ident="f0010"></elsevierMultimedia><p id="par0170" class="elsevierStylePara elsevierViewall">A representative derivative spectrum is shown in <a class="elsevierStyleCrossRef" href="#f0015">Figure 3</a>. Here, both minima and maxima values are nearly found at the same position as seen in <a class="elsevierStyleCrossRef" href="#tbl0005">Table 1</a>, which respectively summarize the absorption and reflectance peaks from each sampling point in Zumpango Lake.</p><elsevierMultimedia ident="f0015"></elsevierMultimedia><elsevierMultimedia ident="tbl0005"></elsevierMultimedia><p id="par0175" class="elsevierStylePara elsevierViewall">This spectral similarity could be interpreted as a consequence of the hyacinth dredging, homogeneously distributed in the water body. The evenly distribution of submerged vegetation is apparent in the <span class="elsevierStyleSmallCaps">landsat</span>-<span class="elsevierStyleSmallCaps">tm</span> satellite image taken in the summer of 2003 after the hyacinth milling process, which has frequently been performed on a regular basis since then (<a class="elsevierStyleCrossRef" href="#f0005">Figure 1</a>).</p><p id="par0180" class="elsevierStylePara elsevierViewall">The spectral signatures show typical characteristics of eutrophic waters, with absorption zones at the 400 -500<span class="elsevierStyleHsp" style=""></span>nm (blue) and 600 – 700<span class="elsevierStyleHsp" style=""></span>nm (red) intervals (<a class="elsevierStyleCrossRef" href="#bib0040">Dekker <span class="elsevierStyleItalic">et al</span>., 1991</a>). Likewise, there are reflectance regions at 550<span class="elsevierStyleHsp" style=""></span>nm (green) and at 710<span class="elsevierStyleHsp" style=""></span>nm (near infrared). The difference in reflectance magnitude can be associated with either a greater depth in the water body or with a lesser volumetric concentration of aquatic vegetation and phytoplankton.</p><p id="par0185" class="elsevierStylePara elsevierViewall">Derivative analysis revealed six absorption peaks over a wide range of wavelengths. Three of these were of particular importance: <span class="elsevierStyleItalic">a)</span> in the interval <a name="p38"></a>400-500<span class="elsevierStyleHsp" style=""></span>nm there was a conspicuous average peak m=<span class="elsevierStyleHsp" style=""></span>437.13 (s=1.19), corresponding to the blue absorption of chlorophyll; <span class="elsevierStyleItalic">b)</span> in the interval 600-700<span class="elsevierStyleHsp" style=""></span>nm, there were other two relevant absorption peaks at the averaged position m<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>632.80 (s<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>1.21) due to water absorption which is in good agreement with peaks found by <a class="elsevierStyleCrossRef" href="#bib0135">Pegau and Zaneveld (1993)</a> and, finally, the peak at m<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>683.86 (s<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>1.38) that can be linked to chlorophyll <span class="elsevierStyleItalic">a</span> when the concentration of this pigment is over 3<span class="elsevierStyleHsp" style=""></span>mg<span class="elsevierStyleHsp" style=""></span>m<span class="elsevierStyleSup">-3</span> (<a class="elsevierStyleCrossRef" href="#bib0050">Gitelson <span class="elsevierStyleItalic">et al</span>., 1993</a>). Additionally, there was a shoulder around 644<span class="elsevierStyleHsp" style=""></span>nm in the red region, which might be related to an inflexion region due, or related, to chlorophyll red absorption.</p><p id="par0190" class="elsevierStylePara elsevierViewall">On the other hand, ten reflectance peaks were revealed by the derivative method, however only two can be associated to phytoplankton and/ or submerged vegetation. These included one in the green region at the averaged position m<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>558.76 (s<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>1.86), which corresponds to chlorophyll <span class="elsevierStyleItalic">a</span> reflectance, and one in the infrared region at the averaged location m<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>706.14 (s<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>1.21), caused by the high reflectance of vegetation at this portion of the electromagnetic spectrum.</p><p id="par0195" class="elsevierStylePara elsevierViewall">The mean value of the integrated energy is 23.09<span class="elsevierStyleHsp" style=""></span>mw<span class="elsevierStyleHsp" style=""></span>nm<span class="elsevierStyleSup">-1</span> sr<span class="elsevierStyleSup">-1</span><span class="elsevierStyleHsp" style=""></span>cm<span class="elsevierStyleSup">-1</span> (s<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>1.92), being higher at sampling point 1 (27.1) and lower at the point 5 (21.4).<a name="p39"></a></p><p id="par0200" class="elsevierStylePara elsevierViewall">Chlorophyll <span class="elsevierStyleItalic">a</span> concentration, expressed as bio-mass, showed a similar and homogeneous spectral trend over the water body extrapolated from the sampling points. <a class="elsevierStyleCrossRef" href="#tbl0010">Table 2</a> shows chlorophyll <span class="elsevierStyleItalic">a</span> concentration values for each sampling site associated to the integrated spectral area. Sampling sites 1 and 2, located at the northern part of the lake, showed the highest Chl <span class="elsevierStyleItalic">a</span> values. This can be explained by the presence of agricultural fields and sewage discharges. Chlorophyll <span class="elsevierStyleItalic">a</span> mean value was of 179.77±21.21<span class="elsevierStyleHsp" style=""></span>mg<span class="elsevierStyleHsp" style=""></span>m<span class="elsevierStyleSup">-3</span>, which is clearly indicative of eutrophic waters, and the correlation coefficient between chlorophyll concentration and spectral area was 0.69. Similar results for urban lakes have been reported elsewhere (e. g., <a class="elsevierStyleCrossRef" href="#bib0110">Martínez and Jáuregui, 2000</a>; <a class="elsevierStyleCrossRef" href="#bib0125">Oliva <span class="elsevierStyleItalic">et al.,</span> 2008</a>).</p><elsevierMultimedia ident="tbl0010"></elsevierMultimedia><p id="par0205" class="elsevierStylePara elsevierViewall">Secchi transparency in the lake averaged 66 (0.06)<span class="elsevierStyleHsp" style=""></span>cm, which corresponds to a mean extinction coefficient of K<span class="elsevierStyleHsp" style=""></span>=<span class="elsevierStyleHsp" style=""></span>2.57 (0.23)<span class="elsevierStyleHsp" style=""></span>m<span class="elsevierStyleSup">-1</span> (<a class="elsevierStyleCrossRef" href="#tbl0010">Table 2</a>); this value can be associated with turbid waters according to Jerlov’s classification (<a class="elsevierStyleCrossRef" href="#bib0095">1976</a>). Sampling site 6 had the maximum value of Secchi transparency, which can be explained by its depth and for being located away of the lake’s border influence.</p><p id="par0210" class="elsevierStylePara elsevierViewall">Trophic State Index values for Chl <span class="elsevierStyleItalic">a</span> and Secchi disk transparency, revealed eutrophic and hyper-eutrophic conditions, respectively (<a class="elsevierStyleCrossRef" href="#bib0020">Carlson, 1983</a>). Thus, the <span class="elsevierStyleSmallCaps">tsi</span> for Secchi disk transparency was 54.1 which corresponds to eutrophic waters and suggests anoxic hypolimnia, whilst <span class="elsevierStyleSmallCaps">tsi</span> value for Chl <span class="elsevierStyleItalic">a</span> was 81.51, classified in the hyper-eutrophic waters interval, characterized by algal scum and few macrophytes (<a class="elsevierStyleCrossRef" href="#bib0020">Carlson, 1983</a>). Moreover and according to <a class="elsevierStyleCrossRef" href="#bib0025">Carlson and Simpson (1996)</a>, since <span class="elsevierStyleSmallCaps">tsi</span>(Chl)<span class="elsevierStyleHsp" style=""></span>><span class="elsevierStyleHsp" style=""></span><span class="elsevierStyleSmallCaps">tsi</span>(SD), a possible explanation for this condition is the presence and dominance of large particles in the lake, which, in the case of Zumpango Lake is represented by the presence of the milled water hyacinth all over the site.</p></span><span id="sec0050" class="elsevierStyleSection elsevierViewall"><span class="elsevierStyleSectionTitle" id="sect0070">Conclusions</span><p id="par0215" class="elsevierStylePara elsevierViewall">Measured spectral curves clearly show the presence of phytoplankton and / or submerged higher plants, mainly water hyacinth (<span class="elsevierStyleItalic">Eichhornia spp</span>) and duckweed (<span class="elsevierStyleItalic">Lemna sp</span>). Zumpango Lake is a unique case among the remnant water bodies in the basin of Mexico because of its homogeneous spectral response. This characteristic is mainly due to a strong wind mixing, which distributes mechanically milled hyacinth.</p><p id="par0220" class="elsevierStylePara elsevierViewall">Water coloration and depth affect the outgoing energy as measured through integrated spectral curves. A good statistical correlation was found between [Chl <span class="elsevierStyleItalic">a</span>] and integrated spectral areas; thus, it implies that a low percentage of light penetration and high chlorophyll <span class="elsevierStyleItalic">a</span> concentration are suitable indicators of eutrophication. Hyperspectral remote sensors offer the possibility of a detailed analysis of the spectral behavior. For a better characterization it is helpful to have ancillary information, allowing anthropogenic and natural influences on continental water bodies to be assessed. <a name="p40"></a></p></span></span>" "textoCompletoSecciones" => array:1 [ "secciones" => array:11 [ 0 => array:3 [ "identificador" => "xres526700" "titulo" => "Abstract" "secciones" => array:1 [ 0 => array:1 [ "identificador" => "abst0005" ] ] ] 1 => array:2 [ "identificador" => "xpalclavsec546930" "titulo" => "Key words" ] 2 => array:2 [ "identificador" => "xpalclavsec546929" "titulo" => "Palabras clave" ] 3 => array:3 [ "identificador" => "xres526701" "titulo" => "Resumen" "secciones" => array:1 [ 0 => array:1 [ "identificador" => "abst0010" ] ] ] 4 => array:2 [ "identificador" => "sec0005" "titulo" => "Introduction" ] 5 => array:2 [ "identificador" => "sec0010" "titulo" => "Study area" ] 6 => array:3 [ "identificador" => "sec0015" "titulo" => "Methods and material" "secciones" => array:4 [ 0 => array:2 [ "identificador" => "sec0020" "titulo" => "Secchi transparency and extinction coefficient k" ] 1 => array:2 [ "identificador" => "sec0025" "titulo" => "Hyperspectral measurements" ] 2 => array:2 [ "identificador" => "sec0030" "titulo" => "Derivative analysis" ] 3 => array:2 [ "identificador" => "sec0035" "titulo" => "Phytoplankton data" ] ] ] 7 => array:2 [ "identificador" => "sec0040" "titulo" => "Trophic state index" ] 8 => array:2 [ "identificador" => "sec0045" "titulo" => "Results and analysis" ] 9 => array:2 [ "identificador" => "sec0050" "titulo" => "Conclusions" ] 10 => array:1 [ "titulo" => "References" ] ] ] "pdfFichero" => "main.pdf" "tienePdf" => true "fechaRecibido" => "2012-10-18" "fechaAceptado" => "2013-07-24" "PalabrasClave" => array:1 [ "en" => array:2 [ 0 => array:4 [ "clase" => "keyword" "titulo" => "Palabras clave" "identificador" => "xpalclavsec546929" "palabras" => array:4 [ 0 => "Análisis hiperespectral" 1 => "Lago de Zumpango" 2 => "eutrofización" 3 => "limnología física" ] ] 1 => array:4 [ "clase" => "keyword" "titulo" => "Key words" "identificador" => "xpalclavsec546930" "palabras" => array:4 [ 0 => "Hyperspectral analysis" 1 => "Zumpango Lake" 2 => "Eutrophication" 3 => "Physical Limnology" ] ] ] ] "tieneResumen" => true "resumen" => array:2 [ "en" => array:2 [ "titulo" => "Abstract" "resumen" => "<span id="abst0005" class="elsevierStyleSection elsevierViewall"><p id="spar0015" class="elsevierStyleSimplePara elsevierViewall">This paper shows a hyperspectral optical analysis of Zumpango Lake, relict of one of the lakes that formerly filled the Basin of Mexico. The spectral signatures are dominated by the presence of phytoplankton and submerged vegetation. Integrated spectral curves have a good statistical correlation with chlorophyll <span class="elsevierStyleItalic">a</span> concentration values. It indicates that submerged vegetation water, mainly hyacinth(<span class="elsevierStyleItalic">Eichhornia spp</span>) and duckweed (<span class="elsevierStyleItalic">Lemna sp</span>), and phytoplankton are homogeneously distributed in the water body, which confers its characteristics of eutrophication.</p></span>" ] "es" => array:2 [ "titulo" => "Resumen" "resumen" => "<span id="abst0010" class="elsevierStyleSection elsevierViewall"><p id="spar0020" class="elsevierStyleSimplePara elsevierViewall">En este artículo se presenta un análisis óptico hiperespectral del Lago de Zumpango, el cual es un relicto de los lagos antiguos que anteriormente llenaban la Cuenca de México. las firmas espectrales están dominadas por la presencia de fitoplancton y por vegetación sumergida. Las curvas espectrales integradas presentan una buena correlación estadística con los valores de la concentración de clorofila <span class="elsevierStyleItalic">a</span>. Esto indica que la vegetación sumergida en el agua, principalmente lirio (<span class="elsevierStyleItalic">Eichhornia spp</span>) y lentejilla (<span class="elsevierStyleItalic">Lemma spp</span>), y el fitoplancton están distribuidos homogéneamente en el cuerpo de agua, lo cual le confiere características de eutrofización.</p></span>" ] ] "multimedia" => array:11 [ 0 => array:7 [ "identificador" => "f0005" "etiqueta" => "Figure 1" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr1.jpeg" "Alto" => 1380 "Ancho" => 1833 "Tamanyo" => 328192 ] ] "descripcion" => array:1 [ "en" => "<p id="sp0005" class="elsevierStyleSimplePara elsevierViewall">Location of Zumpango Lake, State of Mexico.</p>" ] ] 1 => array:7 [ "identificador" => "f0010" "etiqueta" => "Figure 2" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr2.jpeg" "Alto" => 1135 "Ancho" => 1301 "Tamanyo" => 77157 ] ] "descripcion" => array:1 [ "en" => "<p id="sp0010" class="elsevierStyleSimplePara elsevierViewall">Spectral signatures from seven sampling sites in Zumpango Lake, Mexico.</p>" ] ] 2 => array:7 [ "identificador" => "f0015" "etiqueta" => "Figure 3" "tipo" => "MULTIMEDIAFIGURA" "mostrarFloat" => true "mostrarDisplay" => false "figura" => array:1 [ 0 => array:4 [ "imagen" => "gr3.jpeg" "Alto" => 945 "Ancho" => 1300 "Tamanyo" => 67427 ] ] "descripcion" => array:1 [ "en" => "<p id="sp0015" class="elsevierStyleSimplePara elsevierViewall">Typical derivative reflectance spectrum of Zumpango Lake.</p>" ] ] 3 => array:7 [ "identificador" => "tbl0005" "etiqueta" => "Table 1" "tipo" => "MULTIMEDIATABLA" "mostrarFloat" => true "mostrarDisplay" => false "tabla" => array:1 [ "tablatextoimagen" => array:1 [ 0 => array:2 [ "tabla" => array:1 [ 0 => """ <table border="0" frame="\n \t\t\t\t\tvoid\n \t\t\t\t" class=""><thead title="thead"><tr title="table-row"><th class="td" title="table-head " align="center" valign="middle" scope="col" style="border-bottom: 2px solid black">SP \t\t\t\t\t\t\n \t\t\t\t</th><th class="td" title="table-head " align="center" valign="middle" scope="col" style="border-bottom: 2px solid black">Absorption peaks (nm) \t\t\t\t\t\t\n \t\t\t\t</th><th class="td" title="table-head " align="center" valign="middle" scope="col" style="border-bottom: 2px solid black">Reflectance peaks (nm) \t\t\t\t\t\t\n \t\t\t\t</th></tr></thead><tbody title="tbody"><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">1 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">439.5, 495.5, 526.8, 569.5, 634.4, 687.0 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">413.3, 428.0, 455.9, 474.1, 488.9, 556.4, 621.5, 644.0, 652.0, 707.5 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">2 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">436.2, 495.5, 526.8, 569.5, 632.8, 683.9 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">413.3, 426.36, 455.9, 474.1, 488.9, 556.4, 621.5, 644.0, 652.05, 707.5 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">3 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">437.8, 493.9, 526.8, 571.16, 631.2, 683.5 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">413.3, 455.9, 474.1, 488.9, 558.1, 619.9, 644.0, 652.1, 707.5 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">4 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">436.2, 495.5, 526.8, 572.8, 631.2, 683.9 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">413.3, 426.4, 455.9, 470.8, 488.9, 559.7, 645.6, 707.5 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">5 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">437.8, 495.5, 528.5, 571.2, 634.4, 683.5 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">413.3, 457.6, 470.8, 488.9, 559.7, 645.6, 705.9 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">6 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">436.2, 495.5, 528.5, 572.8, 632.8, 682.6 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">413.3, 426.4, 455.9, 474.1, 488.9, 559.7, 645.6, 705.9 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">7 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">436.2, 493.9, 526.9, 572.8, 632.8, 682.6 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="left" valign="middle">413.3, 426.4, 457.6, 474.1, 488.9, 561.3, 647.2, 705.9 \t\t\t\t\t\t\n \t\t\t\t</td></tr></tbody></table> """ ] "imagenFichero" => array:1 [ 0 => "xTab848624.png" ] ] ] ] "descripcion" => array:1 [ "en" => "<p id="spar0005" class="elsevierStyleSimplePara elsevierViewall">Averaged absorption and reflectance peaks and integrated spectral curves from seven sampling points in Zumpango Lake</p>" ] ] 4 => array:7 [ "identificador" => "tbl0010" "etiqueta" => "Table 2" "tipo" => "MULTIMEDIATABLA" "mostrarFloat" => true "mostrarDisplay" => false "tabla" => array:1 [ "tablatextoimagen" => array:1 [ 0 => array:2 [ "tabla" => array:1 [ 0 => """ <table border="0" frame="\n \t\t\t\t\tvoid\n \t\t\t\t" class=""><thead title="thead"><tr title="table-row"><th class="td" title="table-head " align="center" valign="middle" scope="col" style="border-bottom: 2px solid black">S. S \t\t\t\t\t\t\n \t\t\t\t</th><th class="td" title="table-head " align="center" valign="middle" scope="col" style="border-bottom: 2px solid black">S.T. (m) \t\t\t\t\t\t\n \t\t\t\t</th><th class="td" title="table-head " align="center" valign="middle" scope="col" style="border-bottom: 2px solid black">K (m<span class="elsevierStyleSup">-1</span>) \t\t\t\t\t\t\n \t\t\t\t</th><th class="td" title="table-head " align="center" valign="middle" scope="col" style="border-bottom: 2px solid black">[Chl <span class="elsevierStyleItalic">a</span>]<span class="elsevierStyleHsp" style=""></span>mg<span class="elsevierStyleHsp" style=""></span>m<span class="elsevierStyleSup">-3</span><span class="elsevierStyleSup">+</span> \t\t\t\t\t\t\n \t\t\t\t</th><th class="td" title="table-head " align="center" valign="middle" scope="col" style="border-bottom: 2px solid black">IA (mw<span class="elsevierStyleHsp" style=""></span>nm<span class="elsevierStyleSup">-1</span> sr<span class="elsevierStyleSup">-1</span> cm<span class="elsevierStyleSup">-1</span>) \t\t\t\t\t\t\n \t\t\t\t</th></tr></thead><tbody title="tbody"><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">1 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">0.60 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">2.83 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">214.70 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">27.1 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">2 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">0.60 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">2.83 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">205.20 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">22.8 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">3 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">0.65 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">2.61 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">168.72 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">21.9 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">4 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">0.65 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">2.61 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">164.35 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">23.3 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">5 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">0.70 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">2.42 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">175.75 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">21.4 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">6 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">0.80 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">2.12 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">167.20 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">23.3 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">7 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">0.65 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">2.61 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">162.45 \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">21.8 \t\t\t\t\t\t\n \t\t\t\t</td></tr><tr title="table-row"><td class="td" title="table-entry " align="center" valign="middle">µ<span class="elsevierStyleHsp" style=""></span>(σ) \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">0.66 (0.06) \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">2.57 (0.23) \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">179.77 (21.21) \t\t\t\t\t\t\n \t\t\t\t</td><td class="td" title="table-entry " align="center" valign="middle">23.09 (1.92) \t\t\t\t\t\t\n \t\t\t\t</td></tr></tbody></table> """ ] "imagenFichero" => array:1 [ 0 => "xTab848623.png" ] ] ] ] "descripcion" => array:1 [ "en" => "<p id="spar0010" class="elsevierStyleSimplePara elsevierViewall">Secchi transparency (S.T), Extinction Coefficient (K), Chlorophyll a concentration ([Chl <span class="elsevierStyleItalic">a</span>]), and integrated spectral curves (IA) for each sampling site</p>" ] ] 5 => array:6 [ "identificador" => "fq0005" "etiqueta" => "(1)" "tipo" => "MULTIMEDIAFORMULA" "mostrarFloat" => false "mostrarDisplay" => true "Formula" => array:5 [ "Matematica" => "K=0.03+0.0015+∑i34Vidi=1.7D" "Fichero" => "STRIPIN_si1.jpeg" "Tamanyo" => 2510 "Alto" => 35 "Ancho" => 243 ] ] 6 => array:6 [ "identificador" => "fq0010" 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false "mostrarDisplay" => true "Formula" => array:5 [ "Matematica" => "<span class="elsevierStyleSmallCaps">tsi</span>(SD)=60-14.41ln(SD)" "Fichero" => "STRIPIN_si6.jpeg" "Tamanyo" => 1927 "Alto" => 16 "Ancho" => 216 ] ] 10 => array:6 [ "identificador" => "fq0030" "etiqueta" => "(6)" "tipo" => "MULTIMEDIAFORMULA" "mostrarFloat" => false "mostrarDisplay" => true "Formula" => array:5 [ "Matematica" => "<span class="elsevierStyleSmallCaps">tsi</span>(Chl a)=9.81ln(Chl a)+30.6" "Fichero" => "STRIPIN_si7.jpeg" "Tamanyo" => 2241 "Alto" => 16 "Ancho" => 254 ] ] ] "bibliografia" => array:2 [ "titulo" => "References" "seccion" => array:1 [ 0 => array:2 [ "identificador" => "bibs0005" "bibliografiaReferencia" => array:40 [ 0 => array:3 [ "identificador" => "bib0005" "etiqueta" => "Aguirre Gómez, 2001" "referencia" => array:1 [ 0 => array:2 [ "contribucion" => array:1 [ 0 => array:2 [ "titulo" => "Detecting photosynthetic algal pigments in natural populations using a high-spectral-resolution 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| Year/Month | Html | Total | |
|---|---|---|---|
| 2024 October | 17 | 4 | 21 |
| 2024 September | 31 | 8 | 39 |
| 2024 August | 28 | 4 | 32 |
| 2024 July | 15 | 1 | 16 |
| 2024 June | 14 | 3 | 17 |
| 2024 May | 15 | 6 | 21 |
| 2024 April | 13 | 6 | 19 |
| 2024 March | 26 | 6 | 32 |
| 2024 February | 25 | 4 | 29 |
| 2024 January | 30 | 7 | 37 |
| 2023 December | 18 | 12 | 30 |
| 2023 November | 10 | 6 | 16 |
| 2023 October | 27 | 12 | 39 |
| 2023 September | 7 | 2 | 9 |
| 2023 August | 11 | 4 | 15 |
| 2023 July | 15 | 15 | 30 |
| 2023 June | 13 | 5 | 18 |
| 2023 May | 22 | 8 | 30 |
| 2023 April | 9 | 2 | 11 |
| 2023 March | 13 | 6 | 19 |
| 2023 February | 22 | 8 | 30 |
| 2023 January | 17 | 8 | 25 |
| 2022 December | 20 | 4 | 24 |
| 2022 November | 28 | 8 | 36 |
| 2022 October | 20 | 12 | 32 |
| 2022 September | 19 | 7 | 26 |
| 2022 August | 30 | 8 | 38 |
| 2022 July | 30 | 7 | 37 |
| 2022 June | 24 | 12 | 36 |
| 2022 May | 31 | 7 | 38 |
| 2022 April | 34 | 7 | 41 |
| 2022 March | 30 | 11 | 41 |
| 2022 February | 16 | 8 | 24 |
| 2022 January | 39 | 11 | 50 |
| 2021 December | 32 | 8 | 40 |
| 2021 November | 22 | 15 | 37 |
| 2021 October | 42 | 13 | 55 |
| 2021 September | 27 | 9 | 36 |
| 2021 August | 25 | 8 | 33 |
| 2021 July | 10 | 9 | 19 |
| 2021 June | 9 | 10 | 19 |
| 2021 May | 13 | 6 | 19 |
| 2021 April | 8 | 4 | 12 |
| 2021 March | 18 | 8 | 26 |
| 2021 February | 25 | 8 | 33 |
| 2021 January | 24 | 12 | 36 |
| 2020 December | 27 | 6 | 33 |
| 2020 November | 15 | 11 | 26 |
| 2020 October | 10 | 6 | 16 |
| 2020 September | 12 | 9 | 21 |
| 2020 August | 21 | 12 | 33 |
| 2020 July | 12 | 10 | 22 |
| 2020 June | 6 | 4 | 10 |
| 2020 May | 12 | 10 | 22 |
| 2020 April | 16 | 9 | 25 |
| 2020 March | 21 | 6 | 27 |
| 2020 February | 20 | 3 | 23 |
| 2020 January | 19 | 4 | 23 |
| 2019 December | 18 | 5 | 23 |
| 2019 November | 10 | 4 | 14 |
| 2019 October | 16 | 3 | 19 |
| 2019 September | 23 | 12 | 35 |
| 2019 August | 14 | 4 | 18 |
| 2019 July | 23 | 10 | 33 |
| 2019 June | 60 | 19 | 79 |
| 2019 May | 66 | 30 | 96 |
| 2019 April | 34 | 11 | 45 |
| 2019 March | 10 | 5 | 15 |
| 2019 February | 12 | 8 | 20 |
| 2019 January | 8 | 9 | 17 |
| 2018 December | 9 | 4 | 13 |
| 2018 November | 15 | 1 | 16 |
| 2018 October | 26 | 8 | 34 |
| 2018 September | 27 | 5 | 32 |
| 2018 August | 4 | 12 | 16 |
| 2018 July | 14 | 1 | 15 |
| 2018 June | 14 | 3 | 17 |
| 2018 May | 13 | 3 | 16 |
| 2018 April | 5 | 0 | 5 |
| 2018 March | 16 | 0 | 16 |
| 2018 February | 13 | 0 | 13 |
| 2018 January | 6 | 2 | 8 |
| 2017 December | 13 | 0 | 13 |
| 2017 November | 9 | 0 | 9 |
| 2017 October | 18 | 1 | 19 |
| 2017 September | 15 | 1 | 16 |
| 2017 August | 16 | 0 | 16 |
| 2017 July | 25 | 4 | 29 |
| 2017 June | 46 | 7 | 53 |
| 2017 May | 33 | 1 | 34 |
| 2017 April | 17 | 3 | 20 |
| 2017 March | 9 | 40 | 49 |
| 2017 February | 13 | 5 | 18 |
| 2017 January | 10 | 1 | 11 |
| 2016 December | 35 | 8 | 43 |
| 2016 November | 34 | 6 | 40 |
| 2016 October | 47 | 12 | 59 |
| 2016 September | 39 | 1 | 40 |
| 2016 August | 34 | 4 | 38 |
| 2016 July | 35 | 3 | 38 |
| 2016 June | 36 | 10 | 46 |
| 2016 May | 35 | 13 | 48 |
| 2016 April | 36 | 15 | 51 |
| 2016 March | 38 | 16 | 54 |
| 2016 February | 34 | 16 | 50 |
| 2016 January | 33 | 16 | 49 |
| 2015 December | 29 | 16 | 45 |
| 2015 November | 19 | 12 | 31 |
| 2015 October | 46 | 25 | 71 |
| 2015 September | 18 | 8 | 26 |
| 2015 August | 16 | 7 | 23 |
| 2015 July | 15 | 2 | 17 |
| 2015 June | 13 | 2 | 15 |
| 2015 May | 15 | 5 | 20 |
| 2015 April | 22 | 13 | 35 |
| 2015 March | 28 | 10 | 38 |
| 2015 February | 27 | 13 | 40 |
| 2015 January | 19 | 7 | 26 |
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