Towards the use of TRMM PR measurements for the inter-calibration of the South African radar network

South Africa has 11 operating radars, two of which belong to the Water Research Commission (WRC) and the other 9 (all EEC C-band) to the South African Weather Bureau (SAWB). The WRC owns the only dual-wavelength (S- and X - band) MRL-5 radar (using an EEC transmitter) and one Pacer C-band radar.

In August 1998 the Bethlehem Precipitation Research Project (BPRP) introduced a MDV- based weather radar system for South Africa. The MDV format (meteorological data volume) now forms the basis for radar data collection in South Africa. In addition software to merge and display data from multiple radars was developed as well. The hardware and software developments relevant to the system are discussed by Terblanche et al (1994), Mather et al(1997), Terblanche (1996) and Mittermaier and Terblanche (1997).

South Africa lies between 22 and 36 degrees S and has a highly variable rainfall climatology, of which perhaps 25 % is due to the influence of ENSO events on the region. Water resources are of critical importance in the southern African region and the management strategy can be optimized by using as up-to-date rainfall information as possible. Radar rainfall fields in real- time or with a minimal lag can provide such information.

As soon as data from different sources are merged, discrepancies between the data sources become more apparent. These can be hardware dependent (i.e. one radar's sensitivity is better than another's) or calibration dependent. Although some improvements can be made regarding a radar's sensitivity, the latter aspect is where the potential of using TRMM PR measurements is the greatest. Using an independent data source, all ground-based local platforms can be compared to determine how well the calibrations of the individual radars match, in relative terms.

The object of this presentation is to show the progress that has been made to achieve this. Examples of comparisons between TRMM PR and ground-based data from South African radars will be given and some preliminary conclusions on the success of this approach will be made.

Mather G.K., D.E. Terblanche and F.E. Steffens, 1997 : National Precipitation Research Programme : Final Report for the period 1993 - 1996, WRC Rep. 726/1/97, P.O. Box 824, Pretoria, 0001, South Africa.

Mittermaier M.P. and D.E. Terblanche, 1997 : Converting weather radar data to Cartesian space : A new approach using DISPLACE averaging. Water SA, 23, 45-50.

Terblanche D.E., F.O. Hiscutt and D.J. Dicks, 1994 : The upgrading and performance testing of the Bethlehem weather radar. S. Afr. J. Sci., 90, 588-595.

Terblanche D.E., 1996 : A simple digital signal processing method to simulate linear and quadratic responses from a radar's logarithmic receiver. J. Atmos. Ocean Tech., 13(2), 533-538.