Penetration depth of interferometric syntheticsaperture radar signals in snow and ice

Digital elevation models of glaciated terrain produced by the NASA/Jet Propulsion Laboratory (JPL) airborne interferometric synthetic-aperture radar (InSAR) instrument in Greenland and Alaska at the C(5.6 cm wavelength) and L-band (24-cm) frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth, or penetration depth, 5p. On cold polar firn at Greenland summit, 5p 9+2m at Cand 14-+-4m at L-band. On the exposed ice surface of Jakobshavn Isbrae, west Greenland, 5p 1-+2 m at Cand 3-+-3 m at L-band except on smooth, marginal ice where 5p 154-5 m. On colder marginal ice of northeast Greenland, 5p reaches 60 to 120 m at L-band. On the temperate ice of Brady Glacier, Alaska, 5p is 4-+-2 m at Cand 12-+-6 m at L-band, with little dependence on snow/ice conditions. The implications of the results on the scientific use of InSAR data over snow/ice terrain is discussed. and the design and performance estimation of future radar systems. To evaluate the performance of InSAR topographic mapping over snow/tim and ice, the NASA/JPL Topsap instrument (http://airsar.jpl.nasa.gov/) was deployed in Greenland in May 1995 and Alaska in June 1996 to survey outlet glaciers and inland ice areas of varying snow/tim and ice conditions. Data collection was coordinated with overflights by the NASA/Wallops airborne laser altimeter in Greenland [Krabill et al., 1999], and the University of Alaska airborne laser altimeter system in Alaska [Echelmeyer et al., 1996]. Laser altimetry provides an accurate surface reference to evaluate the performance of InSAR topographic mapping.