The range bin numbers in the output of 2A25 are all relative to the Earth's ellipsoid with the ellipsoid range bin corresponding to 79. For example, if the range bin number is 75, its height from the ellipsoid is (79-75)*0.25 = 1.0 km. This number is NOT the height above the actual surface.
For other 2A25 related caveats, please read: http://trmm.gsfc.nasa.gov/2a25.html
Samples of related publications:
- Bolen S. and V. Chandrasekar, 2003, Methodology for aligning and comparing space borne and ground based radar observations, J.Atmos . Ocean Tech, vol 20, No. 5, pp 647-659.
- Liao, L., and R. Meneghini, 2009: Validation of TRMM precipitation radar through comparison of its multiyear measurements with ground-based radar. J. Appl. Meteor. Climatol., 48, 804–817, https://doi.org/10.1175/2008JAMC1974.1.