Chlorophyll retrieval accuracies from satellite and in-situ radiometric measurements in Open Ocean and complex and bloom waters (Conference Presentation)

2019 ◽  
Author(s):  
Samir Ahmed ◽  
Ahmed El-Habashi ◽  
Claudia Duran ◽  
Vincent Lovko ◽  
Stefanos Spiratos
Keyword(s):  
Open Ocean ◽  
Radiometric Measurements

scholarly journals Microwave snow emission modeling uncertainties in boreal and subarctic environments

2015 ◽  
Vol 9 (5) ◽  
pp. 5719-5773
Author(s):  
A. Roy ◽  
A. Royer ◽  
O. St-Jean-Rondeau ◽  
B. Montpetit ◽  
G. Picard ◽  
...  
Keyword(s):  
Grain Size ◽  
Spatial Variability ◽  
Boreal Forest ◽  
Frozen Soil ◽  
Microwave Emission ◽  
Small Scale ◽  
Radiometric Measurements ◽  
Snow Properties ◽  
Modeling Uncertainties

Abstract. This study aims to better understand and quantify the uncertainties in microwave snow emission models using the Dense Media Radiative Theory-Multilayer model (DMRT-ML) with in situ measurements of snow properties. We use surface-based radiometric measurements at 10.67, 19 and 37 GHz in boreal forest and subarctic environments and a new in situ dataset of measurements of snow properties (profiles of density, snow grain size and temperature, soil characterization and ice lens detection) acquired in the James Bay and Umijuaq regions of Northern Québec, Canada. A snow excavation experiment – where snow was removed from the ground to measure the microwave emission of bare frozen ground – shows that small-scale spatial variability in the emission of frozen soil is small. Hence, variability in the emission of frozen soil has a small effect on snow-covered brightness temperature (TB). Grain size and density measurement errors can explain the errors at 37 GHz, while the sensitivity of TB at 19 GHz to snow increases during the winter because of the snow grain growth that leads to scattering. Furthermore, the inclusion of observed ice lenses in DMRT-ML leads to significant improvements in the simulations at horizontal polarization (H-pol) for the three frequencies (up to 20 K of root mean square error). However, the representation of the spatial variability of TB remains poor at 10.67 and 19 GHz at H-pol given the spatial variability of ice lens characteristics and the difficulty in simulating snowpack stratigraphy related to the snow crust. The results also show that for ground-based radiometric measurements, forest emission reflected by the surface leads to TB underestimation of up to 40 K if neglected. We perform a comprehensive analysis of the components that contribute to the snow-covered microwave signal, which will help to develop DMRT-ML and to improve the required field measurements. The analysis shows that a better consideration of ice lenses and snow crusts is essential to improve TB simulations in boreal forest and subarctic environments.

scholarly journals Bromocarbons in the tropical coastal and open ocean atmosphere during the 2009 Prime Expedition Scientific Cruise (PESC-09)

2014 ◽  
Vol 14 (15) ◽  
pp. 8137-8148 ◽  
Author(s):  
M. S. Mohd Nadzir ◽  
S. M. Phang ◽  
M. R. Abas ◽  
N. Abdul Rahman ◽  
A. Abu Samah ◽  
...  
Keyword(s):  
Chlorophyll A ◽  
Statistical Tests ◽  
Open Ocean ◽  
Common Source ◽  
Sampling Point ◽  
Coastal Regions ◽  
Chl A ◽  
June July ◽  
Strait Of Malacca

Abstract. Atmospheric concentrations of very short-lived species (VSLS) bromocarbons, including CHBr3, CH2Br2, CHCl2Br, CHClBr2, and CH2BrCl, were measured in the Strait of Malacca and the South China and Sulu–Sulawesi seas during a two-month research cruise in June–July 2009. The highest bromocarbon concentrations were found in the Strait of Malacca, with smaller enhancements in coastal regions of northern Borneo. CHBr3 was the most abundant bromocarbon, ranging from 5.2 pmol mol−1 in the Strait of Malacca to 0.94 pmol mol−1 over the open ocean. Other bromocarbons showed lower concentrations, in the range of 0.8–1.3 pmol mol−1 for CH2Br2, 0.1–0.5 pmol mol−1 for CHCl2Br, and 0.1–0.4 pmol mol−1 for CHClBr2. There was no significant correlation between bromocarbons and in situ chlorophyll a, but positive correlations with both MODIS and SeaWiFS satellite chlorophyll a. Together, the short-lived bromocarbons contribute an average of 8.9 pmol mol−1 (range 5.2–21.4 pmol mol−1) to tropospheric bromine loading, which is similar to that found in previous studies from global sampling networks (Montzka et al., 2011). Statistical tests showed strong Spearman correlations between brominated compounds, suggesting a common source. Log–log plots of CHBr3/CH2Br2 versus CHBr2Cl/CH2Br2 show that both chemical reactions and dilution into the background atmosphere contribute to the composition of these halocarbons at each sampling point. We have used the correlation to make a crude estimate of the regional emissions of CHBr3 and to derive a value of 32 Gg yr−1 for the Southeast (SE) Asian region (10° N–20° S, 90–150° E). Finally, we note that satellite-derived chlorophyll a (chl a) products do not always agree well with in situ measurements, particularly in coastal regions of high turbidity, meaning that satellite chl a may not always be a good proxy for marine productivity.

scholarly journals An Autonomous Open-Ocean Stereoscopic PIV Profiler

2010 ◽  
Vol 27 (8) ◽  
pp. 1362-1380 ◽  
Author(s):  
Jonah V. Steinbuck ◽  
Paul L. D. Roberts ◽  
Cary D. Troy ◽  
Alexander R. Horner-Devine ◽  
Fernando Simonet ◽  
...  
Keyword(s):  
Flow Direction ◽  
Vertical Plane ◽  
Free Fall ◽  
Open Ocean ◽  
Stereoscopic Particle Image Velocimetry ◽  
Frame Rate ◽  
Energy Estimates ◽  
Seeding Density ◽  
Stereoscopic Piv

Abstract Over the past decade, a novel free-fall imaging profiler has been under development at the Scripps Institution of Oceanography to observe and quantify biological and physical structure in the upper 100 m of the ocean. The profiler provided the first detailed view of microscale phytoplankton distributions using in situ planar laser-induced fluorescence. The present study examines a recent incarnation of the profiler that features microscale turbulent flow measurement capabilities using stereoscopic particle image velocimetry (PIV). As the profiler descends through the water column, a vertical sheet of laser light illuminates natural particles below the profiler. Two sensitive charge-coupled device (CCD) cameras image a 25 cm × 25 cm × 0.6 cm region at a nominal frame rate of 8 Hz. The stereoscopic camera configuration allows all three components of velocity to be measured in the vertical plane with an average spatial resolution of approximately 3 mm. The performance of the PIV system is evaluated for deployments offshore of the southern California coast. The in situ image characteristics, including natural particle seeding density and imaged particle size, are found to be suitable for PIV. Ensemble-averaged velocity and dissipation of turbulent kinetic energy estimates from the stereoscopic PIV system are consistent with observations from an acoustic Doppler velocimeter and acoustic Doppler current profiler, though it is revealed that the present instrument configuration influences the observed flow field. The salient challenges in adapting stereoscopic PIV for in situ, open-ocean turbulence measurements are identified, including cross-plane particle motion, instrument intrusiveness, and measurement uncertainty limitations. These challenges are discussed and recommendations are provided for future development: improved alignment with the dominant flow direction, mitigation of instrument intrusiveness, and improvements in illumination and imaging resolution.

scholarly journals Bromocarbons in the tropical coastal and open ocean atmosphere during the Prime Expedition Scientific Cruise 2009 (PESC 09)

2014 ◽  
Vol 14 (1) ◽  
pp. 953-984 ◽  
Author(s):  
M. S. Mohd Nadzir ◽  
S. M. Phang ◽  
M. R. Abas ◽  
N. Abdul Rahman ◽  
A. Abu Samah ◽  
...  
Keyword(s):  
Chlorophyll A ◽  
Statistical Tests ◽  
Open Ocean ◽  
Common Source ◽  
Sampling Point ◽  
The South ◽  
Coastal Regions ◽  
Chl A ◽  
Strait Of Malacca

Abstract. Atmospheric concentrations of very short-lived species (VSLS) bromocarbons, including CHBr3, CH2Br2, CHCl2Br, CHClBr2, CH2BrCl, were measured in the Strait of Malacca and the South China and Sulu-Sulawesi Seas during a two month research cruise in June/July 2009. The highest bromocarbon concentrations were found in the Strait of Malacca, with smaller enhancements in coastal regions of Northern Borneo. CHBr3 was the most abundant bromocarbon, ranging from 5.2 pmol mol−1 in the Strait of Malacca to 0.94 pmol mol−1 over the open ocean. Other bromocarbons showed lower concentrations, in the range of 0.8–1.3 pmol mol−1 for CH2Br2, 0.1–0.5 pmol mol−1 (CHCl2Br) and 0.1–0.4 pmol mol−1 (CHClBr2). There was no significant correlation between bromocarbons and in situ chlorophyll a. Together the short-lived bromocarbons contribute an average of 8.9 pmol mol−1 (range 5.2–21.4 pmol mol−1) to tropospheric bromine load, which is similar to that found in previous studies (Montzka et al., 2011). Statistical tests showed strong Spearman correlations amongst brominated compounds suggesting a common source. Log-log plots of CHBr3/CH2Br2 vs. CHBr2Cl/CH2Br2 show that both chemical reactions and dilution into the background atmosphere contribute to the composition of these halocarbons at each sampling point. We have used the correlation to make a crude estimate of the regional emissions of CHBr3 and derive a value of 63 Gg yr−1 for the South East (S.E.) Asian region (10° N–20° S, 90–150° E). Finally, we note that satellite-derived chlorophyll a (chl a) products do not always agree well with in situ measurements, particularly in coastal regions of high turbidity, meaning that satellite chl a may not always be a good proxy for marine productivity.

scholarly journals Variation of Summer Oceanic <i>p</i>CO<sub>2</sub> and Carbon Sink in the Prydz Bay Using SOM Analysis Approach

2018 ◽  
Author(s):  
Suqing Xu ◽  
Keyhong Park ◽  
Yanmin Wang ◽  
Liqi Chen ◽  
Qi Di ◽  
...  
Keyword(s):  
Sea Ice ◽  
Open Ocean ◽  
Sea Surface ◽  
Biological Factor ◽  
Prydz Bay ◽  
Co2 Uptake ◽  
Ocean Region ◽  
Co2 Sink ◽  
Shelf Region

Abstract. This study applies a neural network technique to produce maps of oceanic surface pCO2 in the Prydz Bay in the Southern Ocean on a 0.1 longitude × 0.1 latitude grid based on in-situ measurements during the 31th CHINARE cruise for February 2015. The study area was divided into three regions, Open-ocean region, Sea-ice region and Shelf region. The distribution of oceanic pCO2 was mainly affected by physical process in the Open-ocean region where mixing and upwelling became the main controls. While in the Sea-ice region, oceanic pCO2 changed sharply due to the strong change of seasonal ice. For the Shelf region, biological factor was the main control. The weekly oceanic pCO2 was estimated using a self-organizing map (SOM) by four proxy parameters (Sea Surface Temperature, Chlorophyll a concentration, Mixed Layer Depth, and Sea Surface Salinity) to resolve the nonlinear relationships under complicated biogeochemical conditions in Prydz Bay region. The reconstructed oceanic pCO2 coincides well with the in-situ investigated pCO2 from SOCAT, in the root-mean-square error of 22.14 μatm. Prydz Bay was mainly a strong CO2 sink in February 2015 with a monthly averaged uptake of 18.7 &amp;pm; 4.93 TgC. The oceanic CO2 sink is pronounced in the Shelf region due to its lowest oceanic pCO2 with peak biological production. Strong potential anthropogenic CO2 uptake in the Shelf region will enhance the acidification in the deep water of Prydz Bay and affect the deep ocean acidification in the long run since it contributes to the formation of Antarctic bottom water.

scholarly journals Variations in the summer oceanic <i>p</i>CO<sub>2</sub> and carbon sink in Prydz Bay using the self-organizing map analysis approach

2019 ◽  
Vol 16 (3) ◽  
pp. 797-810 ◽  
Author(s):  
Suqing Xu ◽  
Keyhong Park ◽  
Yanmin Wang ◽  
Liqi Chen ◽  
Di Qi ◽  
...  
Keyword(s):  
Sea Ice ◽  
Open Ocean ◽  
Sea Surface ◽  
Prydz Bay ◽  
Self Organizing Map ◽  
Ocean Region ◽  
Co2 Sink ◽  
Shelf Region ◽  
Self Organizing

Abstract. This study applies a neural network technique to produce maps of oceanic surface pCO2 in Prydz Bay in the Southern Ocean on a weekly 0.1∘ longitude × 0.1∘ latitude grid based on in situ measurements obtained during the 31st CHINARE cruise from February to early March 2015. This study area was divided into three regions, namely, the “open-ocean” region, “sea-ice” region and “shelf” region. The distribution of oceanic pCO2 was mainly affected by physical processes in the open-ocean region, where mixing and upwelling were the main controls. In the sea-ice region, oceanic pCO2 changed sharply due to the strong change in seasonal ice. In the shelf region, biological factors were the main control. The weekly oceanic pCO2 was estimated using a self-organizing map (SOM) with four proxy parameters (sea surface temperature, chlorophyll a concentration, mixed Layer Depth and sea surface salinity) to overcome the complex relationship between the biogeochemical and physical conditions in the Prydz Bay region. The reconstructed oceanic pCO2 data coincide well with the in situ pCO2 data from SOCAT, with a root mean square error of 22.14 µatm. Prydz Bay was mainly a strong CO2 sink in February 2015, with a monthly averaged uptake of 23.57±6.36 TgC. The oceanic CO2 sink is pronounced in the shelf region due to its low oceanic pCO2 values and peak biological production.

Improvement of radiation modelling during cloudy sky days using in-situ and satellite measurements. 

2021 ◽  
Author(s):  
Lea Al Asmar ◽  
Luc Musson-Genon ◽  
Eric Dupont ◽  
Karine Sartelet
Keyword(s):  
Solar Radiation ◽  
Wrf Model ◽  
Cloud Fraction ◽  
Satellite Measurements ◽  
Radiation Model ◽  
Radiometric Measurements ◽  
Observational Site ◽  
Radiation Modelling ◽  
The Impact

&lt;p&gt;Solar radiation modelling is important for the evaluation and deployment of solar renewable energy systems. The amount of solar radiation reaching the ground is influenced by geographical parameters (seasons, latitude and local characteristics of the site) and meteorological and atmospheric parameters (like humidity, clouds or particles). Those parameters have important spatio-temporal variations that make solar radiation hard to model.&amp;#160;&lt;/p&gt;&lt;p&gt;Various radiation models exist in literature. Among them, the 1D radiation model part of the computational fluid dynamics software &amp;#8220;Code_Saturne&amp;#8221; estimates the global and direct solar irradiances at the ground. It takes into account the impact of meteorology, atmospheric gas, particles and clouds whose influence is represented using the two-stream approximation.&amp;#160;&lt;/p&gt;&lt;p&gt;The model showed satisfactory results during clear-sky days &amp;#160;but not during cloudy-sky days. It is a common problem in solar radiation modelling, because of the complexity to accurately represent &amp;#160;clouds, which are extremely variable in space and time and have a strong influence on the depletion of solar irradiance. &amp;#160;&lt;/p&gt;&lt;p&gt;In the current study, the estimation of radiation during cloudy-sky days is improved by coupling the 1D radiation model of Code_Saturne with on-site and satellite measurements of the cloud optical properties. Meteorological data are obtained from the Weather Research and Forecasting (WRF) model, aerosol&amp;#8217;s concentrations from the air-quality modelling platform Polyphemus, and on-site measurements from the SIRTA observational site (close to Paris). Two periods are simulated: 'august 2009' and 'year 2014'. It is shown that the introduction of the measured cloud properties in the computation of the surface radiation fluxes leads to a strong reduction of the simulated errors, compared to the case where these properties are derived from the WRF model. &amp;#160; &amp;#160; &amp;#160; &amp;#160; &amp;#160; &amp;#160; &amp;#160; &amp;#160; &amp;#160; &amp;#160;&lt;/p&gt;&lt;p&gt;A sensitivity analysis on the parameters representing clouds in the model is conducted. It enabled us to identify the most influencing parameters - cloud optical thickness (COD) and cloud fraction - and instruments that are sufficient and mandatory for a good description of solar radiation during cloudy-sky days. A fitted model is developed to deduce the COD from liquid water path measurements. Satellite and radiometric measurements could both be used, although satellite measurements are not always available. &amp;#160;For the estimation of cloud fraction, the best results are obtained from shortwave radiometric measurements or from a sky imager. Moreover, large error cases in hourly values of solar fluxes are examined to understand their origin. For a large part of these error cases, there is a high variation within the hour of satellite or in situ measurements, or the presence of low clouds (in more than 50% of these cases in august 2009).&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

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