The retrieval of cloud base heights from MODIS and three-dimensional cloud fields from NASA's EOS Aqua mission
This paper introduces a methodology to retrieve cloud base heights from electro-optical (EO) imagery and demonstrates the approach with MODerate resolution Imaging Spectroradiometer (MODIS) data collected by NASA's EOS Terra mission. In earlier investigations, the value of cloud top heights and total integrated water vapour was demonstrated as constraints in the retrieval of moisture profiles from microwave moisture sounder data. From the analyses of temporally and spatially coincident Defense Meteorological Satellite Program (DMSP) F-11 and NOAA-10 satellite sensor data, the existence of a cloud base signature appeared evident using external knowledge of cloud top temperatures. More recently, simulations were conducted to determine the sensitivity of observed brightness temperatures to variations in cloud base height and other cloud properties. These studies confirmed the presence of a cloud base spectral signature in microwave moisture sounder data for water clouds, when cloud top temperatures are known to an accuracy of about 3-6°C. However, sensitivity studies also demonstrated the impossibility of retrieving cloud base heights over land with the microwave algorithm; therefore, a second algorithm has been developed that relies exclusively upon the information content in EO sensors for retrievals of cloud base height over land surfaces. This paper introduces the new EO cloud base height retrieval methodology, discusses sensitivity analyses that predict the accuracy of retrievals for cases involving single-layered clouds of different types, and provides results for a case study where cloud base height was retrieved from MODIS data collected by the Terra mission. With the development of two complementary cloud base height retrieval methodologies, it is now postulated that useful three-dimensional (3D) cloud analyses of more complicated, multi-layered cloud bases might be retrieved exclusively from remotely sensed, meteorological satellite sensor data using the combined information obtained with both the EO and microwave algorithms. Therefore, an architecture is provided for the retrieval of 3D cloud fields using data collected by the NASA's EOS Aqua mission, the first system to collect all the sensor data required to retrieve 3D cloud fields solely from remotely sensed satellite sensor data.