Though satellite observations are vital in understanding cloud characteristics and the roles of clouds on climate system, the quality assurance of cloud properties observed by satellites is recognized as one of the important tasks in cloud remote sensing community. Cloud observation from surface is useful in validating such satellite cloud products as well as understanding cloud characteristics in more detail by using high temporal resolution data. We developed an algorithm to retrieve cloud optical thickness (COT) and cloud-particle effective radius (CER) by making use of spectral zenith radiances observed by sky radiometer, a ground-based instrument (Khatri et al., 2019). To further address the filter degradation problem while analyzing data of long-term observation, an on-site calibration procedure is proposed, which has a good accuracy compared with standard calibration transfer method.  Except for some narrow domains that fall within COD < 15, the retrieval errors are small for both COD and CER, and the retrieval accuracy for COD is better than that for CER. The cloud properties retrieved from sky radiometer are being used to validate the cloud products of several satellite sensors, such as MODIS (Terra, Aqua), AHI(Himawari-8), and SGLI(GCOM-C).

Figure 1. Mean bias error for retrieved (a) cloud optical thickness and (b) cloud-particle effective radius for assumed errors in natural logarithm of calibration constant by ±1%, surface albedo by ±0.025, and precipitable water content by ±1.0 cm. For detail, see the publication.

 

Publication

Khatri, P., H. Iwabuchi, T. Hayasaka, H. Irie, T. Takamura, A. Yamazakai, A. Damiani, H. Letu, and Q. Kai (2019), Retrieval of cloud properties from sky radiometer observed spectral zenith radiances, Atmos. Meas. Tech., 12,6037-6047,doi:10.5194/amt-12-6037-2019.