L- and C-band SAR Interferometry analysis of the Wieliczka Salt Mine area (UNESCO Heritage Site, Poland)
Davide Oscar Nitti(1), Fabio Bovenga(2), Alberto Refice(2), Janusz Wasowski(3), Domenico Conte(1) and Raffaele Nutricato(1)
(1) Dipartimento di Fisica - Politecnico di Bari, Via Amendola 173, 70126 BARI, Italy
(2) CNR ISSIA, Via G. AMENDOLA 122/D-O, 70126 BARI, Italy
(3) CNR IRPI, Via G. AMENDOLA 122/I, 70126 BARI, Italy
This work presents the first results of the interferometric processing of ALOS-PALSAR FBS SLC images, concerning ground deformations in the Wieliczka Salt Mine area. Wieliczka, a town located 14 km SE of Cracow, is home to a unique salt mine, over 700 years old, one of the best known tourist attractions in Poland.
First Persistent Scatterers SAR Interferometry analysis on this area has been recently derived  by processing several tens of ERS satellite images covering the period 1992-2000. Results revealed the presence of a few kilometres long subsiding zone corresponding very well to the extent of the underground salt mine. No useful data were obtained in peripheral parts of the mine (rural areas) due to scarcity of PS targets.
Therefore, the present work extends the analysis by exploiting ALOS-PALSAR data especially for the neighbouring rural areas, because of the L-band higher penetration coefficient on the ground and the consequent lower temporal decorrelation in vegetated areas w.r.t. C-band radar data. Furthermore, the use of L-band InSAR data should allow to detect faster movements such as the sudden subsidence events reported in the early 1990’s.
L-band InSAR monitoring is feasible since a periodic revisit of the area is guaranteed by JAXA. Indeed, at least two Fine Beam Ascending acquisitions per year are expected according to the actual PALSAR acquisition plan.
We present results obtained from HH Single Polarization Mode – 34.3° Off-Nadir look angle SAR images. Significant differences were observed between the PRF values of the PALSAR FBS acquisitions available. Therefore, an initial resampling of the images in azimuth direction was required in order to uniform their PRF values.
The night acquisition time of FBS PALSAR images mitigates the atmospheric phase screen in each interferogram generated. The relatively high coherence shown by the interferograms allows an easier unwrapping of the differential interferometric phase, aiding further investigations on the spatial statistical properties of the atmospheric signal.
In the paper, considerations concerning some processing aspects of ALOS data are reported, as well as a preliminary comparison between L-band and C-band differential interferometric phase behaviour. We also provide a preliminary evaluation of the feasibility of the use of PALSAR data for relatively slow subsidence monitoring in the Wieliczka Salt Mine area.
 J. Wasowski et al. Satellite interferometry reveals spatial patterns of subsidence in the ancient Wieliczka Salt Mine (unesco Heritage Site, Poland). In Proceedings of FRINGE 2007, Frascati, Italy, Nov. 26–30, 2007.