This lookup-equation provides the approximate1 for use in the radar equation. This lookup-equation is most helpful in the context of calculating the Signal-to-Noise of a Synthetic Aperture Radar.
^ Performance Limits for Synthetic Aperture Radar - Second Edition. Sandia National Laboratories, Albuquerque, NM. Printed February 2006.
This equation, Two-Way Atmospheric Loss Rate Lookup (Radar), references 1 page