Cloud Effective Emissivity Retrievals Using Combined Ground-Based Infrared Cloud Measuring Instrument and Ceilometer Observations

Lei Liu,Qi Wang,Yi Wu,Zhencong Niu,Ting Zhang

doi:10.3390/rs10122033

Abstract

In this paper, a new inversion procedure for cloud effective emissivity retrievals using a combined ground-based infrared cloud measuring instrument with ceilometer was developed. A quantitative sensitivity and performance analysis of the proposed method was also provided. It was found that the uncertainty of the derived effective emissivity was mainly associated with errors on the measurement radiance, the simulated radiance of clear sky and blackbody cloudy sky. Furthermore, the retrieval at low effective emissivity was most sensitive to the simulated clear sky radiances, whereas the blackbody cloudy sky radiance was the prevailing source of uncertainty at high emissivity. This newly proposed procedure was applied to the measurement taken in the CMA Beijing Observatory Station from November 2011 to June 2012 by the whole-sky infrared cloud-measuring system (WSIRCMS) and CYY-2B ceilometer. The cloud effective emissivity measurements were in good agreement with that of the MODIS/AQUA MYD06 Collection 6 (C6) cloud products. The mean difference between them was 0.03, with a linear correlation coefficient of 0.71. The results demonstrate that the retrieval method is robust and reliable.

Highlights

Clouds play a fundamental role in maintaining the Earth’s energy balance. Cloud properties such as cloud cover, cloud base height (CBH), and cloud type have been measured by human observers for a long time, there are still plenty of shortcomings
We focused on the cloud effective emissivity estimation by using a combined ground-based infrared cloud imager and a ceilometer approach
The ground-based infrared cloud imager used in this paper was the whole-sky infrared cloud-measuring system (WSIRCMS), which is a ground-based passive sensor that uses an uncooled microbolometer detector array to measure downwelling atmospheric radiance in the range of 8–14 μm wavelength bands [15]

Summary

Introduction

Clouds play a fundamental role in maintaining the Earth’s energy balance. cloud properties such as cloud cover, cloud base height (CBH), and cloud type have been measured by human observers for a long time, there are still plenty of shortcomings. The transition from humans to sensors for observing clouds would be a valuable achievement In this process, the ground-based infrared cloud measuring systems have attracted much attention because they can be operated continuously during day and night with a constant sensitivity. The difference in true-CBHs obtained by ceilometers and blackbody-like-CBHs from IR cloud measuring systems can be used to retrieve the cloud effective emissivity. Based on this principle, Garnier et al [10] showed a satellite-based example for the purpose of retrieving high-level cloud effective emissivity using the combined dataset of the Imaging Infrared Radiometer (IIR) and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Cases of inversion results and the statistical results of several months are shown and discussed in Section 4 before ending with the conclusions

Specifications of the Instruments

Principles of Cloud Effective Emissivity Retrieval

Cloud Effective Emissivities for Different Cloud Base Height