Retrieval of Water Constituents from Hyperspectral In-Situ Measurements under Variable Cloud Cover—A Case Study at Lake Stechlin (Germany)
"> Figure 1
<p>Flow chart illustrating the set of measurements and methodology applied in this study. All abbreviations and acronyms are defined in <a href="#sec2dot3-remotesensing-10-00181" class="html-sec">Section 2.3</a>, <a href="#sec2dot4-remotesensing-10-00181" class="html-sec">Section 2.4</a>, <a href="#sec2dot5-remotesensing-10-00181" class="html-sec">Section 2.5</a> and <a href="#sec2dot6-remotesensing-10-00181" class="html-sec">Section 2.6</a>, and are listed at the end of the paper.</p> "> Figure 2
<p>Photographs taken in the direction of the sun illustrating the sky conditions during the times when hyperspectral sets of measurements (M1–M9) were recorded.</p> "> Figure 3
<p>(<b>a</b>) Comparison of Chl-<span class="html-italic">a</span> concentration from in-water irradiance measurements (Ramses setup) with results from <span class="html-italic">bbe</span> probe scans with fixed sensor depth. (<b>b</b>) Retrieval results with varied sensor depth <span class="html-italic">z</span>. Two dots at a given depth represent two measured sets of 30 spectra each.</p> "> Figure 4
<p>(<b>a</b>) Comparison of average <math display="inline"> <semantics> <mrow> <msubsup> <mi>E</mi> <mi>d</mi> <mo>+</mo> </msubsup> </mrow> </semantics> </math> (<span class="html-italic">λ</span>) spectra for different shares of clouds (M3: sun behind clouds, M8: sun visible). (<b>b</b>) Changes in the magnitude of irradiance (integrated over 400 to 700 nm) illustrating the variability in the illumination conditions. (<b>c</b>) standard deviation of <math display="inline"> <semantics> <mrow> <msubsup> <mi>E</mi> <mi>d</mi> <mo>+</mo> </msubsup> </mrow> </semantics> </math>(<span class="html-italic">λ</span>) normalized to average <math display="inline"> <semantics> <mrow> <msubsup> <mi>E</mi> <mi>d</mi> <mo>+</mo> </msubsup> </mrow> </semantics> </math>(<span class="html-italic">λ</span>) for “cloudy” measurements M1–M3 (black line) and all sets of measurements (grey line).</p> "> Figure 5
<p>(<b>a</b>) Variability of radiance reflectance spectra over water; solid lines represent the mean values of the corresponding measurement series and the filled area represents the respective standard deviation per series. (<b>b</b>) Example of a reflectance series (M4) modeled with variable <span class="html-italic">g<sub>dsr</sub></span> and <span class="html-italic">d<sub>r</sub></span> parameters (approach G).</p> ">
Abstract
:1. Introduction
2. Materials and Methods
2.1. Overview of Measurements and Methodology in This Study
2.2. Test Site and Measurement Conditions
2.3. Water Constituents and Vertical Profiles
2.4. Hyperspectral Measurements
2.5. Models for Hyperspectral Data Analysis
2.5.1. Downwelling Irradiance above Water
2.5.2. Downwelling Irradiance in Water
2.5.3. Reflections at the Water Surface
2.5.4. Remote Sensing Reflectance
2.6. Water Constituent Retrieval
2.6.1. Water Constituent Retrieval from In-Water Irradiance
2.6.2. Water Constituent Retrieval from above-Water Radiance Reflectance
3. Results and Discussion
3.1. Water Constituents and Phytoplankton Community
3.2. Water Constituent Retrieval from Downwelling Irradiance Spectra under Water
3.3. Water Constituent Retrieval from Radiance Reflectance Spectra above Water
4. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
List of Acronyms and Symbols (Alphabetical Order)
aCDOM | Absorption coefficient of CDOM |
aCDOM+p | Absorption coefficient by colored dissolved and particulate matter |
α | Ångström exponent of aerosol scattering |
AOT | Aerosol optical thickness |
aph(*) | (specific) Absorption coefficient of phytoplankton |
bTSM(*) | (specific) Scattering coefficient of TSM |
bb,TSM(*) | (specific) Backscattering coefficient of TSM |
β | Turbidity coefficient |
CChla | Concentration of Chl-a |
CTSM | Concentration of TSM |
CDOM | Colored dissolved organic matter |
Chl-a | Chlorophyll-a |
dr | Cloud offset to surface reflectance |
Ed | Downwelling irradiance |
Edd | Downwelling irradiance component from direct sunlight |
Edsa | Downwelling irradiance component from light scattered by aerosols (Mie scattering) |
Edsr | Downwelling irradiance component from light scattered by molecules (Rayleigh scattering) |
fdd | Relative intensity of direct component of downwelling irradiance |
fdd | Relative intensity of diffuse component downwelling irradiance |
fdsa | Relative intensity of aerosol component of downwelling irradiance |
fdsr | Relative intensity of Rayleigh component of downwelling irradiance |
FWHM | Full width at half maximum |
gdd | Reflection factor for direct component of downwelling irradiance |
gdsa | Reflection factor for aerosol component of downwelling irradiance |
gdsr | Reflection factor for contribution of Rayleigh component of downwelling irradiance |
Hoz | Scale height of ozone |
HPLC | High performance liquid chromatography |
λ | Wavelength |
Lsky | Sky radiance |
Lu | Upwelling radiance |
LWCC | Liquid waveguide capillary cell |
PSICAM | Point-source integrating cavity absorption meter |
r | Spearman’s correlation coefficient |
Rrs | Remote sensing reflectance |
Rsurf | Surface reflectance |
RSR | Remote sensing ratio |
SCDOM | Spectral slope parameter of CDOM absorption |
σ | Standard deviation |
T | Temperature |
TSM | Total suspended matter |
VIS | Visible wavelength range |
WASI | Inversion software “water color simulator” |
WV | Scale height of precipitable water in the atmosphere |
z | Sensor depth |
− | Reference to measurement in water |
+ | Reference to measurement above water |
3C | Three component surface reflectance model |
4C | Four component surface reflectance model |
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SCDOM (nm−1) | aCDOM(440) (m−1) | CChla (µg L−1) | CTSM (mg L−1) | bb,TSM (m−1) | bTSM (m−1) |
---|---|---|---|---|---|
0.017 ± 0.002 1 | 0.21 ± 0.01 1 | 14.4 ± 0.5 3 | 2.05 ± 0.17 | 0.026 ± 0.01 | 2.14 ± 0.09 |
0.017 ± 0.002 2 | 0.25 ± 0.01 2 | 12.4 ± 1.0 4 |
Fixed Surface Parameters | Varied Parameters | M1 | M2 | M3 | M4 | M5 | M6 | M7 | M8 | M9 | |
---|---|---|---|---|---|---|---|---|---|---|---|
gdsr, gdsa = 0.32 gdd = 0.02 | dr = 0 | fdd, fds | A | − | − | − | + | + | − | − | + | + |
fdd, fds = 1 | gdsa, gdsr, gdd = 0 | dr | B | + | + | + | − | − | + | − | − | + |
fdd, fds = 1 | gdsa, gdsr = 0 |dr = 0 | gdd | C | − | − | − | − | − | − | − | − | − |
fdd, fds = 1 | gdsa, gdd = 0 |dr = 0 | gdsr | D | − | − | − | − | − | − | − | − | − |
fdd, fds = 1 | gdsr, gdd = 0 |dr = 0 | gdsa | E | − | − | − | − | − | − | − | + | − |
fdd, fds = 1 | gdsa = 0 | gdsr, gdd | F | + | + | + | + | + | + | + | + | + |
fdd, fds = 1 | gdsa = 0 | gdsr, dr | G | + | + | + | + | + | + | + | + | + |
fdd, fds = 1 | gdsa = 0 | gdd, gdsr, dr | H | + | + | + | + | + | + | + | + | + |
fdd, fds = 1 | dr = 0 | gdd, gdsa, gdsr | I | + | + | + | + | + | + | + | + | + |
fdd, fds = 1 | gdd, gdsa, gdsr, dr | J | + | + | + | + | + | + | + | + | + |
No surface reflections | - | K | − | − | − | − | − | − | − | − | − |
B | F | G | H | I | J | |
---|---|---|---|---|---|---|
# surface parameters | 1 | 2 | 2 | 3 | 3 | 4 |
Average residua | 1.57 × 10−5 | 1.06 × 10−5 | 9.56 × 10−6 | 9.47 × 10−6 | 8.78 × 10−6 | 9.28 × 10−6 |
σ ( (µg L−1)) | 1.21 | 0.60 | 0.66 | 0.79 | 1.10 | 0.82 |
σ ( (mg L−1)) | 0.23 | 0.21 | 0.20 | 0.21 | 0.21 | 0.19 |
(m−1) | 0.00 ± 0.00 | 0.11 ± 0.03 | 0.09 ± 0.04 | 0.09 ± 0.03 | 0.08 ± 0.03 | 0.10 ± 0.05 |
r (|) | 0.77 | 0.22 | 0.44 | 0.53 | 0.55 | 0.34 |
r (|) | −0.02 | −0.36 | −0.12 | −0.17 | −0.55 | −0.44 |
r (|) | 0.55 | 0.61 | 0.47 | 0.41 | 0.10 | −0.42 |
r (|surf)° | 0.57 (dr) | −0.29 (gdd) | −0.50 (gdsr) | −0.52 (gdsr) | 0.67 (gdsa) | −0.46 (gdsr) |
r (|surf)° | 0.55 (dr) | 0.71 (gdsr) | 0.65 (dr) | 0.61 (dr) | 0.66 (gdsa) | 0.44 (gdsa) |
r (|surf)° | 0.67 (dr) | 0.84 (gdsr) | 0.69 (dr) | 0.64 (dr) | 0.51 (gdsr) | 0.79 (gdsr) |
CChla (µg L−1) | CTSM (mg L−1) | aCDOM(440) (m−1) | |
---|---|---|---|
Reflectance inversion approach (G) | 9.1 ± 0.7 | 1.4 ± 0.2 | 0.09 ± 0.04 |
Water sample | 14.4 ± 0.5 | 2.1 ± 0.1 | 0.21/0.25 ± 0.01/0.01 * |
Fluorescence probe | 12.4 ± 1.0 | - | - |
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Göritz, A.; Berger, S.A.; Gege, P.; Grossart, H.-P.; Nejstgaard, J.C.; Riedel, S.; Röttgers, R.; Utschig, C. Retrieval of Water Constituents from Hyperspectral In-Situ Measurements under Variable Cloud Cover—A Case Study at Lake Stechlin (Germany). Remote Sens. 2018, 10, 181. https://doi.org/10.3390/rs10020181
Göritz A, Berger SA, Gege P, Grossart H-P, Nejstgaard JC, Riedel S, Röttgers R, Utschig C. Retrieval of Water Constituents from Hyperspectral In-Situ Measurements under Variable Cloud Cover—A Case Study at Lake Stechlin (Germany). Remote Sensing. 2018; 10(2):181. https://doi.org/10.3390/rs10020181
Chicago/Turabian StyleGöritz, Anna, Stella A. Berger, Peter Gege, Hans-Peter Grossart, Jens C. Nejstgaard, Sebastian Riedel, Rüdiger Röttgers, and Christian Utschig. 2018. "Retrieval of Water Constituents from Hyperspectral In-Situ Measurements under Variable Cloud Cover—A Case Study at Lake Stechlin (Germany)" Remote Sensing 10, no. 2: 181. https://doi.org/10.3390/rs10020181
APA StyleGöritz, A., Berger, S. A., Gege, P., Grossart, H. -P., Nejstgaard, J. C., Riedel, S., Röttgers, R., & Utschig, C. (2018). Retrieval of Water Constituents from Hyperspectral In-Situ Measurements under Variable Cloud Cover—A Case Study at Lake Stechlin (Germany). Remote Sensing, 10(2), 181. https://doi.org/10.3390/rs10020181