The Total Electron Content From InSAR and GNSS: A Midlatitude Study

The total electron content (TEC) measured from the
interferometric synthetic aperture radar (InSAR) and froma dense
network of global navigation satellite system (GNSS) receivers are
used to assess the capability of InSAR to retrieve ionospheric information,
when the tropospheric contribution to the interferometric
phase is reasonably negligible.With this aim, we select three nighttime
case studies over Italy and investigate the correlation between
TEC from advanced land observing satellite-phased array type
L-band synthetic aperture radar (ALOS-PALSAR) and from the
Rete Integrata Nazionale GPS (RING) network, the latter considered
as the reference true ionospheric TEC. To retrieve the TEC
variability from ALOS-PALSAR, we first investigate the correlation
between the integral of the azimuth shifts and the interferometric
phase in the absence of ground motions (e.g., earthquakes)
and/or heavy rain events. If correlation exists (as in two out of three
case studies under investigation), we can assume the tropospheric
contribution to the interferometric phase as negligible and theTEC
variability from L-band InSAR can be retrieved. For these two case
studies, the comparison between the TEC from the InSAR images
and from the RING network is quite encouraging as the correlation
coefficient is R ∼ 0.67 in the first case and R ∼ 0.83 in the second
case. This result highlights the potential to combine InSAR and
GNSS experimental measurements to investigate small-scale spatial
variability of TEC, in particular over regions scarcely covered
by ground-based GNSS receivers.