Satellite Products Generated At

Kelkar (1995) has furnished an exhaustive review of quantitative products available from INSAT data. INSAT Meteorological Data Processing System (IMDPS) computes the following numerical products:

1. Cloud Motion Vectors (CMVs)

2. Quantitative Precipitation Estimates (QPEs)

3. Outgoing Long-wave Radiation (OLR)

4. Vertical Temperature Profiles (VTPRs)

5. Sea Surface Temperatures (SSTs)

CMVs, now also termed as atmospheric motions vectors (AMVs), computed from a triplet of satellite scans are disseminated operationally on Global Telecommunication System (GTS) for international consumption. Since the emphasis in the tropics is on the winds, the CMVs find relevance in the analysis of wind field. They have significant impact on the accuracy of numerical models. Though no systematic validation studies of CMVs computed from INSAT data have been carried out, limited studies made by ECMWF in this regard indicate that the quality of this product has shown some improvement. The problems in the derivation of high quality CMVs in the region of active convective disturbances however, still continuing. There are no CMVs in the areas characterized by deep convection and height assignment is also leading to problems.

A large number of schemes have been developed over the years to infer the precipitation estimates from satellite pictures. Since in the tropics, there is preponderance of convective clouds, cloud history methods are of relevance for determination of QPEs. The arkin algorithm (Rao et al., 1989) is being applied to derive operationally large-scale precipitation estimates on daily, weekly and monthly basis. Rainfall is used both as an input in the numerical model scheme for physical initialization and also for verifications of model predicted precipitation. The NWP schemes are unable to account adequately for the diabetic heating.

SSTs are derived from IR Channel (10.5-12.5^m) data from INSAT. A major anomaly in the accurate derivation of SST field is due to attenuation by the moisture in the overlying column, which is compounded by the fact that it is a single broad band channel data. Retrieval of SST during the monsoon season is badly affected due to heavy clouding. Though the seasonal gradients in the SST field are brought out, the accuracy is doubtful.

The Outgoing Longwave Radiation (OLR) is calculated using physical/ statistical algorithm on the IR window channel data received three hourly at IMDPS. Regular OLR derivation have been in progress since 1986. OLR has come out to be a proxy parameter for many of the research applications. OLR data derived from INSAT IR band is being operationally fed to NCMRWF, New Delhi where it is used in their schemes for physical initialization.

Khanna and Kelkar (1993) have described the system for derivation of temperature soundings of the atmosphere over the Indian region using satellite data. They employed physical retrieval method and generated regression estimates using SSU and MSU channels as initial guess. The high resolution sounding data from IMDPS is being assimilated in numerical models at IMD and NCMRWF.

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