中国海洋水色卫星传感器COCTS HY-1D产品初步评价

Preliminary performance of the COCTS onboard HY-1D satellite in the global ocean

卫星遥感产品的真实性评价对利用遥感产品开展应用研究具有重要的意义。本文利用全球典型的长期固定平台现场测量数据对中国自主海洋水色卫星HY-1D所搭载的水色水温扫描仪COCTS(COCTS HY-1D)遥感反射率(R_(rs))和叶绿素a(Chl-a)产品进行了评价,并在全球尺度上通过与国际主流海洋水色卫星传感器的产品进行了进一步的对比分析。结果表明,COCTS HY-1D R_(rs)产品与现场测量R_(rs)数据吻合较好,可见光波段相关系数在0.91—0.98,各波段平均绝对百分比误差平均值约为22.9%。相较于国际主流海洋水色卫星传感器MODIS Aqua与现场数据各波段平均绝对百分比误差平均值约为20.5%的比较结果,产品精度相当;在全球尺度上,与MODIS Aqua相比,R_(rs)产品分布趋势一致,数值大小一致,相关系数在蓝光波段较高,可达0.94,各波段相关系数平均值为0.84。Chl-a产品相关系数为0.85,高于MODIS Aqua与VIIRS-SNPP的Chl-a产品的相关系数0.76。整体上,COCTS HY-1D可以提供与国际主流海洋水色卫星传感器质量相当的水色产品,能够进行准确的海洋水色遥感观测。

The Chinese Ocean Color and Temperature Scanner(COCTS)onboard HY-1D satellite(COCTS HY-1D)was launched on June 11,2020.However,the performance of COCTS HY-1D has not yet been completely evaluated.In this study,the performance of COCTS HY-1D was first evaluated by comparing satellite derived remote sensing reflectance(R_(rs))with in situ measurements collected at four AERONET-OC sites and two Chinese long-term platforms.Initially,the in situ data at four AERONET-OC sites were acquired to evaluate the performance of COCTS HY-1D in the global coastal waters.AERONET-OC is an ocean color component of the AERONET and provides long-term high-quality in situ normalized water leaving radiance(L_(wn))measured by an autonomous radiometer system on an offshore fixed platform to support the calibration and validation of satellite ocean color sensors in coastal waters.Muping and Dong'ou sites were constructed by the China National Satellite Ocean Administration Service(NSOAS),and the data were processed following the same procedure as that of the AERONET-OC data processing scheme.The COCTS HY-1D Level 1B data covering AERONET-OC sites and two long-term platforms between 1 August 12020 and 31 January 312021 in cloud-free days were acquired from NSOAS and processed to Level 2 R_(rs)and Chl-a concentration products.Furthermore,R_(rs)and Chl-a concentration comparison with two well-calibrated ocean color sensors(i.e.,MODIS Aqua and VIIRS-SNPP)were made to evaluate the performance of COCTS HY-1D on the global scale.Additionally,the COCTS HY-1D Level 1B daily global dataset between December 7 and 14,2020 were also required from NSOAS,processed to Level 2,and binned to Level 3 daily and 8-day 9-km data products by using the spatial-temporal binning algorithms developed by NASA.MODIS Aqua and VIIRS-SNPP Level 3 global binned daily and 8-day 9-km R_(rs)and Chl-a concentration data collected between December 7 and 14,2020 were acquired from NASA GSFC.The statistics used in this study included correlation coefficient(r),Root Mean Square Error(RMSE),Mean Absolute Percentage Error(MAPE),and mean bias(mBias).Results demonstrated that COCTS HY-1D-derived R_(rs)agreed well with the in situ data at all wavelengths with the correlation coefficient r of visible bands between 0.91 and 0.98 and up to 0.98 and Mean Absolute Percentage Error(MAPE)of 22.9%.The product's accuracy is comparable to the average MAPE of 20.5%between MODIS Aqua and in situ data.At the global scale,the COCTS HY-1D-derived R_(rs)and chlorophyll concentration were consistent with MODIS Aqua products with a mean correlation coefficient ranging from 0.84 and to 0.95.The correlation coefficient of Chl-a is 0.85,which is higher than 0.76 between MODIS Aqua and VIIRS-SNPP.Nevertheless,the satisfactory R_(rs)was derived from COCTS HY-1D at the global scale compared with the in situ measurements or well-calibrated MODIS Aqua and VIIRS-SNPP products.COCTS HY-1D can provide high quality ocean color products comparable with the international mainstream ocean color satellite sensors,and therefore can carry out stable and accurate ocean color remote sensing observation.