ISPRS Commission II, Vol.34, Part 3A „Photogrammetric Computer Vision“, Graz, 2002 
  
METHODICAL ALTERNATIVES TO THE GLACIER MOTION MEASUREMENT FROM 
DIFFERENTIAL SAR INTERFEROMETRY 
A.I. Sharov *, K.Gutjahr *, F. Meyer ^, M. Schardt * 
Institute of Digital Image Processing, Joanneum Research, Graz, Austria - (aleksey.sharov, karlheinz.gutjahr)@joanneum.at 
? Chair for Photogrammetry and Remote Sensing, Technical University Munich, Germany - franz.meyer@bv.tu-muenchen.de 
Commission III, WG III/3 
Key words: Differential SAR Interferometry, Phase Gradient, Glacier Motion, Velocity, Geodetic Survey 
ABSTRACT: 
Algorithmic variations to the glacier motion estimation from differential SAR interferometry are discussed in the present paper. Two 
efficient albeit relatively simple algorithms for modelling glacier dynamics using spaceborne INSAR data have been devised and 
tested as alternatives to the conventional DINSAR approach. Neither of the algorithms involves the procedure of interferometric 
phase unwrapping, thus excluding the areal error propagation and improving the modelling accuracy. In general, they remain feasible 
even under significant phase noise. An original gradient approach (GINSAR) to differential processing of repeat-pass SAR 
interferograms based on the calculation of interferometric phase gradients, the generation of glacier slope maps and the analysis of 
differences between multitemporal slope maps provides global and fast solutions to unsupervised glacier change detection and ice 
motion estimation. A transferential approach is based on the interferometric measurement of the fast-ice translation forced by the 
glacier flow and provides good reference values on the glacier frontal velocity and velocity gradients for the GINSAR technique. A 
comparative analysis of the results obtained by different techniques was performed and algorithmic singularities were discussed. The 
  
revealed differences of up to 40% between the GINSAR velocities and those surveyed in the field are explained. 
1. PRELIMINARY REMARKS 
The high level of scientific and industrial interest in satellite 
radar interferometry (INSAR) has not been extinguished over 
the past 10 years. The INSAR method is greatly valued by 
experts studying glacier dynamics, because of its notable data 
availability and astonishing sensitivity to ice motion / 
deformation. Spectacular results using multitemporal repeat- 
pass interferograms from ERS-1/2 and RADARSAT satellites 
for glacier-flow measurement, strain rate estimation and 
detection of rapid glacier changes are reported every year 
(Bamler&Hartl, 1998; Forster etal., 1999; Rabus & Fatland, 2000) 
Differential interferometry (DINSAR), the methodological 
variant based on differencing between two SAR interferograms 
obtained at different times over the same glacier, became 
especially popular among glaciologists investigating glacier 
mass flux and mass balance. Although the theory of 
conventional DINSAR is well established (Gabriel et al., 1989; 
Joughin et al., 1996), the technological perfection in converting 
differential SAR interferograms to a surface-velocity vector 
field has yet to be completed. There are several approaches to 
solving the principal task of differential interferometry, i.e. 
distinguishing between the impacts of surface topography and 
surface displacement on the interferometric phase. A concise 
classification and characterisation of algorithmic variations to 
differential interferometric processing of SAR imagery can be 
found in (Wegmüller & Strozzi, 1998). 
Generally speaking, all known DINSAR algorithms are based 
on practically the same complement of operations including co- 
registration of interferograms, phase scaling and subtraction 
and, inevitably, the procedure of interferometric phase 
unwrapping; the latter is reputed to be the most sophisticated 
and problematic calculus in interferometric signal processing. 
Apart from the algorithmic complexity and computational load, 
this integral procedure is error-prone and frequently becomes 
impossible, at least locally, because of complex glacier 
topography and significant phase noise at glacier fronts, walls 
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and tops. Moreover, in conventional DINSAR the operation of 
phase integration has to be performed twice, i.e. in each of two 
original interferograms. This leads to error propagation. In our 
experience, none of the available phase-unwrapping algorithms 
such as branch-cut, least squares or minimum-cost flow 
techniques, provide reliable and detailed surface models of test 
glaciers, even if high-quality interferograms are used. The 
procedure of phase unwrapping is currently reputed by experts 
to be a break-point in the INSAR technology; the quality of 
consecutive products cannot be guaranteed (H.Raggam, 
personal communication 2002). 
Our recent research has thus been focused on designing and 
testing alternative algorithms for glacier motion estimation and 
variational analysis of ice velocities without phase unwrapping. 
Several alternative algorithms using 
e  transferential approach to the ice motion interpretation 
in single interferograms and 
e gradient approach to the glacier surface modelling and 
glacier velocity measurement 
were developed and tested using the ERS-1/2-INSAR data 
obtained over large tidewater glaciers in the European Arctic. 
The present paper describes these new algorithms and their 
singularities, and provides the most interesting results of tests 
and validations. The tachometric accuracy was verified by 
mutual comparison of models obtained by alternative 
techniques and compared with results of geodetic observations 
from the field campaign 2001. 
2. STANDARD DINSAR TECHNIQUE FOR THE GLACIER 
MOTION ESTIMATION AND ITS LIMITATIONS 
Compared to other remote sensing techniques, the DINSAR 
method has the one wonderful advantage: it allows quite small 
glacier changes / motions in the centimetre range to be detected 
and measured from satellite SAR images with a nominal ground 
resolution of several tens of meters. A full separation between