Dr. P. V. Nagamani Profile

Dr. P. V. Nagamani

at National Remote Sensing Ctr

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Author

Publications (2)

Proceedings Article | 7 May 2016 Paper

High-resolution shipboard measurements of phytoplankton: a way forward for enhancing the utility of satellite SST and chlorophyll for mapping microscale features and frontal zones in coastal waters

Christy Jenkins, Joaquim Goes, Kali McKee, Helga do R. Gomes, Robert Arnone, Menghua Wang, Michael Ondrusek, P. Nagamani, T. Preethi Latha, K. Rao, V. Dadhwal

Proceedings Volume 9878, 98780U (2016) https://doi.org/10.1117/12.2225875

KEYWORDS: Satellites, Pulmonary function tests, Carbon, Remote sensing, Algorithm development, Data modeling, Luminescence, Ecosystems, Particles, Satellite communications

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Coastal eddies, frontal zones and microscale oceanographic features are now easily observable from satellite measurements of SST and Chl a. Enhancing the utility of these space-borne measurements for biological productivity, biogeochemical cycling and fisheries investigations will require novel bio-optical methods capable of providing information on the community structure, biomass and photo-physiology of phytoplankton associated on spatial scales that match these features. This study showcases high-resolution in-situ measurements of sea water hydrography (SeaBird CTD®), CDOM (WetLabs ALF®), phytoplankton functional types (PFTs, FlowCAM®), biomass (bbe Moldaenke AlgaeOnlineAnalyzer® and WetLabs ALF®) and phytoplankton photosynthetic competency (mini-FIRe) across microscale features encountered during a recent (Nov. 2014) cruise in support of NOAA's VIIRS ocean color satellite calibration and validation activities. When mapped against binned daily, Level 2 satellite images of Chl a, K_d490 and SST over the cruise period, these high-resolution in-situ data showed great correspondence with the satellite data, but more importantly allowed for identification of PFTs and water types associated with microscale features. Large assemblages of phytoplankton communities comprising of diatoms and diatom-diazotroph associations (DDAs), were found in mesohaline frontal zones. Despite their high biomass, these populations were characterized by low photosynthetic competency, indicative of a bloom at the end of its active growth possibly due to nitrogen depletion in the water. Other prominent PFTs such as Trichodesmium spp., Synechococcus spp. and cryptophytes, were also associated with specific water masses offering the promise and potential that ocean remote sensing reflectance bands when examined in the context of water types also measurable from space, could greatly enhance the utility of satellite measurements for biological oceanographic, carbon cycling and fisheries studies.

Proceedings Article | 7 May 2016 Paper

Optimization of spectral bands for ocean colour remote sensing of aquatic environments

P. V. Nagamani, Aneesh Lotliker, R. Navalgund, V. Dadhwal, K. Rao, T. Srinivasa Kumar, T. Preethi Latha

Proceedings Volume 9878, 987808 (2016) https://doi.org/10.1117/12.2225870

KEYWORDS: Sensors, Remote sensing, Signal to noise ratio, Atmospheric corrections, Remote sensing, Absorption, Luminescence, Near infrared, Aerosols, Short wave infrared radiation, MODIS

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Selection of central wavelengths, bandwidths and the number of spectral bands of any sensor to be flown on a remote sensing satellite is important to ensure discriminability of targets and adequate signal-to-noise ratio for the retrieval of parameters. In recent years, a large number of spectral measurements over a wide variety of water types in the Arabian Sea and the Bay of Bengal have been carried out through various ship cruises. It was felt pertinent to use this precious data set to arrive at meaningful selection of spectral bands and their bandwidths of the ocean colour sensor to be flown on the forthcoming Oceansat-3 of ISRO. According to IOOCG reports and studies by Lee and Carder (2002) it is better for a sensor to have ~15 bands in the 400-800 nm range for adequate derivation of major properties (phytoplankton biomass, colored dissolved organic matter, suspended sediments, and bottom properties) in both oceanic and coastal environments from observation of water color.

In this study, ~417 hyper-spectral remote-sensing reflectance spectra (spectral range varies from ~380-800 nm) covering different water types like open, coastal, mid coastal and near coastal waters have been used to identify the suitable spectral bands for OCM-3. Central wavelengths were identified based on the results obtained from hyper-spectral underwater radiometer measurements of Rrs, HPLC pigments and spectrometer analyzed absorption spectra for all the above water types. Derivative analysis has been carried out from 1st to 5th order to identify the inflection and null points for better discrimination / identification of spectral peaks from the in situ R_rs spectra. The results showed that open ocean and coastal ocean waters has spectra peaks mostly in the blue, green region; turbid coastal waters has maximum spectral peaks in the red region. Apart from this, the spectral peaks were identified in the red region for the chlorophyll fluorescence in the open ocean and coastal waters. Based on these results 13 spectral bands were proposed in the VNIR region for the upcoming OCM-3 sensor. In order to obtain water leaving radiances from the measurements at spacecraft platform, it is necessary to do atmospheric correction we need to have spectral bands in the NIR and above regions. Hence, a set of bands 3 bands in the NIR and SWIR region were proposed for OCM-3 to address the atmospheric correction related issues.

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