Publications

Qing, S; Cui, TW; Tang, JW; Song, QJ; Liu, RJ; Bao, YH (2022). An optical water classification and quality control model (OC_QC model) for spectral diffuse attenuation coefficient. ISPRS JOURNAL OF PHOTOGRAMMETRY AND REMOTE SENSING, 189, 255-271.

Abstract
Spectral diffuse attenuation coefficient of down-welling irradiance (Kd(lambda)) is a fundamental optical parameter for water color and of significance for heat budget calculation, photosynthesis modeling and carbon sequestration. Uncertainties exist in both in situ measured and satellite derived Kd(lambda), therefore, evaluation of its data quality is essential. In addition, optical water classification of Kd(lambda) is still limited. To address these issues, we proposed an optical water classification and quality control model (OC_QC model) based on a globally collected high-quality in situ Kd(lambda) data. The model consists of the reference Kd(lambda) spectra for 7 optical water types (OWT, ranging from clear open ocean water to highly turbid water) and a scoring system. An individual Kd(lambda) spectrum can be assigned an OWT and quality control score (QC score) with this model. The performance of the OC_QC model is tested with independent in situ Kd(lambda) spectra from the turbid coastal water (Bohai Sea) and clear oceanic water (Indian Ocean). Questionable or erroneous Kd(lambda) spectra can be identified, suggesting the model's robustness. The model was also evaluated with the Medium Resolution Imaging Spectrometer (MERIS) Level-2 and the Moderate Resolution Imaging Spectroradiometer (MODIS) Level-3 Kd(lambda) data in the Bohai Sea, Yellow Sea, East China Sea and South China Sea. Satellite derived maps clearly showed the spatial and temporal variations of OWTs and QC scores, and the regions of low-quality Kd(lambda) were reasonably extracted. Global maps of Kd(lambda)-based optical water types and corresponding QC scores were also obtained with OC_QC model. With the quality controlled Kd(lambda) data, the retrieval accuracy of Secchi disk depth was improved. The retrieval accuracies of Chlorophyll-a concentration and total seawater absorption coefficient were also improved with the Kd(lambda) optical water classification based algorithms. The OC_QC model would be valuable for evaluating Kd(lambda) data (especially the operational global Kd(lambda) products), investigation of water optical properties, and development and merging of bio-optical algorithms.

DOI:
10.1016/j.isprsjprs.2022.05.006

ISSN:
1872-8235