Improved Radiometric and Spatial Capabilities of the Coastal Zone Imager Onboard Chinese HY 1C Satellite for Inland Lakes
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 <italic>in situ</italic> 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 <inline formula> <tex math notation="LaTeX"$R_{\mathrm {rs} /tex math>/inline formula> from CZI measurements was evaluated. 6SV derived <inline formula> <tex math notation="LaTeX"$R_{\mathrm {rs} /tex math>/inline formula> showed higher accuracy than that of FLAASH, validated by the synchronous <italic>in situ</italic> <inline formula> <tex math notation="LaTeX"$R^{2} \simeq 0.50$ /tex math>/inline formula> absolute percent difference (APD) <inline formula> <tex math notation="LaTeX"\simeq ~20$ /tex math>/inline formula> and OLI derived <inline formula> <tex math notation="LaTeX"$R_{\mathrm {rs} /tex math>/inline formula> <inline formula> <tex math notation="LaTeX"$R^{2} \simeq ~0.75$ /tex math>/inline formula> APD <inline formula> <tex math notation="LaTeX"\simeq ~5$ /tex math>/inline formula> Finally, the abilities of CZI to observe cyanobacterial bloom, suspended particular matter (SPM) and chlorophyll <inline formula> <tex math notation="LaTeX"$a$ /tex math>/inline formula> (Chl<inline formula> <tex math notation="LaTeX"$a$ /tex math>/inline formula> 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 <inline formula> <tex math notation="LaTeX"$R^{2} 0.68$ /tex math>/inline formula> root mean square error (RMSE) 9.68 mg/L, APD 13.52% for SPM) While CZI only has four wide bands, Chl<inline formula> <tex math notation="LaTeX"$a$ /tex math>/inline formula> 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.
IEEE Geoscience and Remote Sensing Letters