Verification of pointing and ranging is straight-forward for NCAR ground-based radars, and is done as a routine part of system data quality assurance. In cases where azimuth or range are not quite accurate in the raw data, corrections are made available for use by all ATD software, thereby protecting a user from problems created by these errors. Corrections detailed in this section should be used by anyone processing raw field data with their own routines, and care should be taken to apply these corrections in the proper sense (+/-).
The pointing and ranging of ATD radars is not always exactly correct in the raw field data. Verification of ranging involves the location of appropriate hard targets, both in the radar data and on the ground, an activity that cannot be done until the radar system is properly set-up and collecting data. Full system readiness does not usually occur with much leeway prior to the start of an experiment, and personnel who verify the position and nature of hard targets (through site visits) are not generally available for this task until after the start of data collection. This results in a need to apply corrections (usually small!) to the data after appropriate ranging and pointing checks are done.
Primary verification of pointing is done through "shooting the sun", and is generally quite accurate. This procedure involves following the sun with the radar antenna (transmitter "off"), and finding the azimuth and elevation of the "brightest" solar return. These angle determinations are compared to the expected position of the sun (for the particular time of day and site location). Solar alignment checks are made prior to the start of project data collection, and irregularly throughout a project; adjustments to the radar pedestal are made if there is the need. Solar alignment produces pointing accuracies of about +/- .2 degrees. Solar measurements cannot, however, be used for range verification, and do not give a good indication of possible pointing errors when the radar is slewing across the sky at more typical operational speeds.