A Bispectral Method for Cloud Parameter Determination

Abstract

A technique is presented for determining cloud heights and amounts through the use of simultaneous. infrared and visible satellite radiance data. A set of simultaneous equations are developed which solve for cloud-top temperature (Tcld) and cloud amount (Acld) within the geometric field of view of the sensor. The cloud height is determined by comparing Tcld to upper air soundings, An error analysis is also presented showing the accuracy that can he obtained in Tcld and Acld when uncertainties exist in the measured visible and infrared radiances and in the assumptions required. Actual satellite measurements taken from the NOAA Scanning Radiometer (SR) are input into the technique and run for three specific geographical locations during several seasons where ground-based cloud observations are available. Results show an rms error in cloud amount of 0.2 and in cloud height of 0.5 km for a 75 km?75 km area for all cloud types except cirrus. For this case we have developed alternate solutions which account for the optical depth and emissivity problems associated with cirrus. The modified method was successfully tested on a few cirrus cases showing a reduction in the rms error in cloud height by 1.5 km to an rms error of 1.1 km. Applications of the bispectral method include determining cloud parameters for vertical temperature sounders, solo energy studies, aircraft operations and global earth energy budgets.