A 3-STEP CLOUD CLEARING PROCEDURE FOR INFRARED SOUNDER MEASUREMENTS

A new cloud clearing procedure applied to High-resolution Infrared Radiation Sounder (H1RS/2) radiance measurements is presented, based on knowledge of the typical statistical features of both clear and cloud contaminated radiance fields and on the application of some well known techniques for the statistical handling of data. The procedure consists of three sequential steps. In the first, the clear sky latitudinal gradient is restored using statistical correlation among HIRS/2 and MSU measurements. In the second step the scene variability (i.e. the dynamics along the longitudinal gradient) is retrieved by a discrete Fourier developments and a recursive Kalman filter. Finally, the characteristic smoothness of clear fields is introduced using a low-pass filter (third step). Applications of the whole filtering technique to measured HIRS/2 channel 5, 6 and 7 brightness temperatures are discussed and its performance is checked by comparing sets of filtered and stimulated data. © 1990 Taylor & Francis Group, LLC.