incorrect read of nyquist velocity and range resolution for specific NEXRAD files

[adokter]

Two related problems, exemplified in certain NEXRAD files, e.g. file KLOT20080905_002257_V03.gz:

• Range resolution is read from the ray information provided by RSL_get_first_ray_of_volume() using the reflectivity volume, such that the range resolution is always taken from the first lowest-elevation reflectivity sweep. As a result, the range resolution is read incorrectly if there is a change in range resolution at higher elevation scans. Higher elevation sweeps may have larger range bins, causing these higher elevations scans to projected incorrectly (at too close range / too low altitude). The range resolution should be read for each sweep individually.
• Nyquist velocity is always taken from the reflectivity data of a given sweep. As a result, incorrect Nyquist velocity might be read, because Nyquist velocity of the reflectivity sweep can differ from the radial velocity sweep. Older NEXRAD files may have reflectivity sweeps collected with different PRFs, one short-range matching the radial velocity sweep, and one additional long-range. RSL reads only the long-range sweep, causing a mismatch in PRF and Nyquist velocity between the radial velocity and reflectivity scan parameter collected at the same elevation. A solution to this problem is to take the Nyquist velocity from the radial velocity data.

[adokter]

fixed by #167