Retrieval Of Chlorophyll Concentrations In The Ocean By Using CALIPSO Lidar Signal Below The Ocean Surface

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)，an instrumenton the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation(CALIPSO)，can produce simultaneous co-aligned pluses at1064nm and532nm.The research shows that the active sensor CALIOP can get parameters of clouds andaerosols in the atmosphere, and at the same time, the532nm laser pulses canpenetrate the ocean surface, and then obtain the backscatter information about waterbody. In this paper, the CALIPSO level1data at532nm is used to calculate theCALIOP transient response function, and then is corrected for the use of the study ofthe relationship between the particulate backscattering coefficient and chlorophyllconcentrations in the ocean.The CALIOP measurements at532nm from land surface during2008, based onthe Tail-to-Peak ratio method proposed by Y. Hu, are used to calculate therelationship between the peak signal and signals adjacent it. As a result, the relationsshow a great difference in winter and summer in northern hemisphere, but thecharacteristic of data in spring and autumn agrees well with that in winter. In addition,the distribution statistics of about43.6%samples in winter are the same as that of thesamples in summer in northern hemisphere, the statistics of the other56.4%samplesare consistent with the samples on Antarctic and Greenland, where the land surfaceare almost entirely covered by snow and ice all the year round. It can be concludedthat the different relationships of samples in winter and summer are caused by snowand ice. By using the method mentioned by Li, the transient response of CALIOPPMT is calculated. The results show that different land surfaces have the sametransient response function, regardless the land covered by snow or ice.Because of the transient response, when the backscatter signal is received by thePMT, the energy of peak signal spreads to several bins after the peak. As a result the transient response of CALIOP affect the waveform, making the sampled signal morebigger than that it should be. So，the attenuated underwater backscatter should becorrected by using the transient response function F. In the ocean, it is a reasonableassumption that the particle optical backscattering is mainly coursed by phytoplanktonpigments. In this paper, the CALIPSO level1version3products, combining withwind speed data provided by Advanced Microwave Scanning Radiometer for theEarth Observing System (AMSR-E) and annual averaged chlorophyll concentrationdata and diffuse attenuation coefficient data provided by Moderate ResolutionImaging Spectrometer (MODIS), are used to get the CALIPSO lidar signal below theocean surface and signal corrected by using the transient response function at532nm.The result shows that, in the global ocean area, the correlation coefficient betweenchlorophyll concentration and CALIOP particulate backscatter coefficients are0.54and0.58for uncorrected and corrected underwater data respectively. In the oceanarea from60°S to40°N, the correlation coefficients are0.72and0.79respectively.