Antenna Scanning Sequence

The Suncal utility uses the antenna library to control the antenna scan.

We normally expect that the antenna angles are input to the RVP processor, which is the case for IRIS. The current UTC time is taken from the local computer system's time to compute the sun's position. You must check that the time is correct to within a few seconds.

A Suncal PPI sector scan is created and starts centered at the sun's initial position minus half of the elevation span given in the suncal.conf file. This scan starts below the sun's position and scans back and forth at the resolution requested in the file.

You control the PRF, sample size, range bin spacing, and number of bins. This task is not angle synced. The azimuth scan speed is half that implied by the requested PRF and sample size. The data nearest to the desired azimuths are stored.

The first defined pulse width of the signal processor is used. The quality of the sun calibration should not be affected by different pulse widths because the sun is broad band, just like the noise. The recorded data is SNR (which in IRIS is dBT with range normalization turned off).

To account for the sun's movement during the scan, some corrections need to be made so the output is similar to a non-moving radiation source.

To do this, the sun's position is recalculated at the start of each sweep. The change in the sun's position is subtracted from all angles for that sweep. This correction is output to the terminal window during each sweep when run interactively.

For example, if the sun moved towards the horizon by 0.10° during the Suncal task and there were 5 sweeps the elevation angle increment of each sweep would be numerically decreased by approximately 0.02°. Similar angle corrections are done in the azimuth direction.