An empirical model for the assessment of DEM accuracy degradation due to vertical atmospheric stratification

This paper reports on the implications of vertical refractivity profiles in the troposphere on the quality of Digital Elevation Models and surface deformation maps derived from synthetic aperture radar (SAR) interferometry. A representative set of 1460 radiosondes acquired over one year in the Netherlands is used to obtain statistics for the differential delays between the two acquisition dates, and apply these to simulate 1-day and k × 35 day intervals corresponding with ERS-1/2 orbit characteristics. It is shown that differential delays can amount up to more than 1 cm for height intervals of 500 meters or more. For a 2 km height interval and an interferometric baseline of 80 m such delays result in an height error of 180 m. It is not possible to find a generally valid correction scheme for these delays using surface meteorological measurements. Only in situ vertical profile measurements such as radiosondes can be applied to correct for these errors. To obtain a first order indication of the extent of these effects on the accuracy of products derived from radar interferometry, the rms of the delay is determined as a function of height. An empirical expression for the rms is presented.