The Measurement of Height and Slope of Isobaric Surfaces With an Airborne Radar Altimeter

The aeronautical use of electronic altimeters is to measure the absolute clearance of an aircraft above the earth's surface. In the support of atmospheric research, accurate high-range altimeters, in conjunction with accurate static pressure and navigation data, can also provide a means for measuring the heights of constant-pressure surfaces. From the derivatives of the measurements, surface slopes and dynamical quantities such as the geostrophic wind may be obtained. This paper describes the operational and research use of a highaltitude pulse-type radar altimeter system installed on the NCAR Sabreliner for jet stream research. An error analysis for "D-value," derived from radar altitude and pressure measurements, gave an estimated error of ��6.0 m, which surpasses measurements from conventional balloon soundings or satellite-derived height analyses. For a case study of jet stream dynamics, the above error in D-value corresponded to an error of ��5% in the computed geostrophic wind.