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.
