A sequential estimation approach to cloud-clearing for satellite temperature sounding

Abstract

Temperature sounding of the troposphere using satellite-borne infrared radiometers is complicated by the effects of clouds on the measured radiances. If accurate products are to be obtained these effects must first be detected and, if possible, corrections must be made for them in the retrieval procedures. This is normally done by converting the measured radiances to the 'clear-column' values which would be observed from the same atmospheric profile in the absence of cloud-a process known as 'cloud-clearing'.In this paper a review of cloud-clearing methods is presented. Then a new approach to cloud-clearing, based on the principles of optimal estimation, is developed and applied to data from HIRS (the High-resolution Infrared Radiation Sounder) on the TIROS-N/NOAA satellite series.Preliminary estimates of clear-column radiances and their expected errors are obtained at each HIRS spot by one of a number of methods, depending on the cloud characteristics. The properties of horizontal consistency expected in the clear-column radiance field are then employed to improve the initial estimates using a sequential estimation procedure. This scheme is intended for implementation in the Local Area Sounding System of the Meteorological Office, which provides satellite soundings of high horizontal resolution for use in operational weather forecasting. Details of the new scheme, and of the old scheme which it replaces, are given. The improvements in clear-column radiances are demonstrated by comparing the products of the old and new schemes with clear-column radiances derived from coincident data of AVHRR (the Advanced Very High Resolution Radiometer). 1349

Assimilating INSAT‐3D Thermal Infrared Window Imager Observation With the Particle Filter: A Case Study for Vardah Cyclone

“…(2) Use of cloud‐cleared radiances in assimilation. Generation of cloud‐cleared radiances is a procedure that transforms cloudy radiances into equivalent clear radiances (Eyre & Watts, ; Heilliette & Garand, ; Li et al, , ). (3) Assimilation of observations taken from those channels that are not affected by clouds.…”

The assimilation of cloud‐affected infrared satellite radiances for numerical weather prediction

“…These methods are far from ideal, since only small proportions of the available soundings are being exploited. As an alternative to rejecting cloudy radiances, it is possible to assimilate so-called 'cloudcleared' radiances (Eyre and Watts, 1987;Li et al, 2005), 738 E. G. PAVELIN ET AL. where variations in cloud cover in neighbouring FOVs are used to eliminate the cloud signal and reconstruct the clear-sky radiance. However, the assumption of homogeneous cloud characteristics implicit in the cloudclearing technique is unlikely to be satisfied in the majority of cases.…”

An improved method for detecting clear sky and cloudy radiances from AVHRR data

“…the High Resolution Infrared Radiation Sounder, HIRS, on the same satellite as the AVHRR). Clear sky radiances are normally required in order to obtain accurate temperature profiles (Eyre and Watts 1987). Conversely, to infer cloud properties from the radiances as outlined by Kriebel (1986), cloud-filled fields of view must be identified.…”