Improved Radiometric and Spatial Capabilities of the Coastal Zone Imager Onboard Chinese HY-1C Satellite for Inland Lakes

摘要

The coastal zone imager (CZI) onboard HY-1C satellite provides a new data source to monitor the lake environments. Here, we provided a preliminary evaluation for the applications of CZI on inland lakes and a comparison with the in situ , Landsat-8 operational land imager (OLI), and Sentinel-2 multispectral instrument (MSI) measurements. First, the in-orbit signal-to-noise ratios (SNRs) were estimated based on homogenous ocean pixels. SNRs of CZI reached ~200:1 in the visible bands and ~150:1 at the near-infrared bands, which are comparable with the OLI and slightly higher than those of the MSI. Then, the performance of 6SV and fast line-of-sight atmospheric analysis of hypercubes (FLAASH) models on the retrievals of remote sensing reflectance ( $R_{mathrm {rs}}$ ) from CZI measurements was evaluated. 6SV-derived $R_{mathrm {rs}}$ showed higher accuracy than that of FLAASH, validated by the synchronous in situ ( $R^{2} simeq 0.50$ , absolute percent difference (APD) $simeq ~20$ %) and OLI-derived $R_{mathrm {rs}}$ ( $R^{2} simeq ~0.75$ , APD $simeq ~5$ %). Finally, the abilities of CZI to observe cyanobacterial bloom, suspended particular matter (SPM), and chlorophyll- $a$ (Chl $a$ ) were assessed. CZI-derived, the area of cyanobacterial bloom and SPM, showed good agreements with the results yielded by the OLI and MSI data on May 24, 2019, in Lake Taihu ( $R^{2} = 0.68$ , root-mean-square error (RMSE) = 9.68 mg/L, APD = 13.52% for SPM). While CZI only has four wide bands, Chl $a$ derived by CZI using an empirical algorithm was relatively consistent with MSI-derived values. CZI demonstrated a decent performance in monitoring the environments of large lakes, and it is expected to add the bands for atmospheric correction and further works in the small-medium lakes in the future.