C. Delacourt et al., TROPOSPHERIC CORRECTIONS OF SAR INTERFEROGRAMS WITH STRONG TOPOGRAPHY- APPLICATION TO ETNA, Geophysical research letters, 25(15), 1998, pp. 2849-2852
The accuracy of spaceborne geodetic techniques, including SAR interfer
ometry, is limited by the time and spatial variation and altitude depe
ndance of the propagation delay of electomagnetic waves in the lower t
roposphere, particularly in mountainous areas. In this paper, we use a
1D model developed for tropospheric corrections of GPS and DORIS meas
urements to correct SAR data. The differential tropospheric delay is c
omputed at each pixel of the interferogram from ground temperature, hu
midity and pressure using two empirical parameters calibrated from sev
eral radio-soundings acquired in various latitude and climate conditio
ns. It is shown that with such a model. given the 3300 meters topograp
hy of Etna, tropospheric variations call generate up to 4 pi phase rot
ations between the top and the bottom of the volcano. In 16 out, of th
e 20 interferograms processed with images acquired between August 1992
and October 1993, correction of the tropospheric effect reduces the n
umber of fringes associated with the 1991-93 eruption from previous es
timates. The remaining deformation is consistant with a deforming sour
ce located at a depth of 14+/-1 km. During the second half of the erup
tion; the subsidence rate at the top of the volcano is roughly stable
at 13+/-3 mm/month. These values are in good agreement with tiltmeter
data collected on Etna during the same period and with the estimated v
olume of erupted material. No significant deformation can be observed
during the last month of eruption. Inflation of the volcano seems to r
esume immediately after the end of the eruption at a rate of 3 mm/mont
h.