PROGRESS

During the two SIR-C/X-SAR missions SRL-1 (9 to 20 April 1994) and SRL-2 (30 September to 10 October 1994) extensive field measurements were carried out on glaciers and on ice-free parts of the test site. The measurements included:

During both SRL-1 and SRL-2:
- deployment and geodetic measurement of corner reflectors (1.25 to 1.8 m leg length) on glaciers,
- measurement of snow depth, density, grain size, dielectric constant, stratification, temperature in snow pits,
- surface roughness profiles of snow and ice,
- meteorological measurements,
- mapping of snow extent,
Additional measurements during SRL-1:
- backscattering of snow at 5 GHz and 35 GHz HH, VV, HV, VH,
- emission of snow at 21 and 35 GHz, H and V,
Additional measurements during SRL-2:
- backscattering of bare soil and alpine grassland at 5.3 GHz and 10.3 GHz HH, VV, HV, VH,
- measurements of soil humidity and surface roughness.
Measurements throughout the year:
- hourly mean runoff of two basins in the central part of the test site,
- ice ablation and accumulation for determination of glacier mass balance,
- meteorological stations.

During SRL-1 the glaciers were covered by dry winter snow, the air temperature at 3000 m was below -10° C, and snowfall was observed during several days. At lower elevations the snow-structure was more complex, and the snowpack was partly humid. During SRL-2 the meteorological conditions changed drastically; the mean daily air temperature dropped by 12° C during the campaign, resulting in significant changes of snow properties and backscattering signatures on the glaciers.

All data, which had been acquired over the test site, were processed and delivered. We obtained the following scenes:

SRL-1, SIR-C (SLC): DT 14.2 (10-04-94), DT 46.1 (12-04-94), DT 78.0 (14-04-94),
SRL-1, X-SAR (SSC, MGD, GTC) : DT 14.2 (10-04-94), DT 18.21 (10-04-94), DT 34.31 (11-04-94), DT 46.1 (12-04-94), DT 78.0 (14-04-94),
SRL-2, SIR-C (SLC), X-SAR (SSC, MGD, GTC) : DT 14.2 (1-10-94), DT 18.21 (1-10-94), DT 34.31 (2-10-94), DT 46.1 (3-10-94), DT 78.1 (5-10-94).

Polarimetric signatures and frequency dependence of backscattering of snow cover, glaciers, and ice-free areas, including vegetated and un-vegetated terrain, were investigated and related to field data of target properties. The analysis included investigations of angular behavior of backscattering properties and studies of temporal changes. Significant short-term changes were observed over snow and ice during SRL-2 at X- and C-band, whereas the seasonal changes in snow and ice properties resulted in pronounced backscattering differences between SRL-1 and SRL-2 at all 3 frequencies. Supervised and unsupervised methods were applied for classification, based on various combinations of backscattering parameters.


SIGNIFICANT RESULTS

- During both SRL-1 and SRL-2 a near real time analysis was carried out over glaciers to determine the accumulation and ablation areas and estimate glacier mass balance.

- The signature analysis clearly demonstrates the importance of multifrequency and polarimetric data for separating different snow and ice regimes on glaciers and for mapping accumulation and ablation areas. L- or C-band co- and cross-polarized channels in combination with X-band were found to be of main importance for this application.

- The maps of accumulation and ablation areas, derived from SIR-C/X-SAR data of SRL-2, show low ratios of accumulation to ablation areas, and consequently significant loss of mass during summer 1994 for all glaciers of the Ötztaler Alpen. Good agreement was found for the mass balance estimated from the SRL-2 data in comparison with field measurements, carried out on two glaciers in the test site for the period 1 October 1993 to 30 September 1994.

Snow Studies in the Innsbruck Region

The region surrounding Innsbruck was covered by the same swathes of the ascending orbits as the test site Ötztal. During SRL-1 the mountain slopes above Innsbruck were covered by humid snow, an intense snowfall event was observed between DT 46.1 and DT 78.0. This enables studies of different snow conditions than at the high alpine site. Snow properties and soil humidity were measured in the field.

For the Innsbruck region so far the following X-SAR data (MGD ) were obtained:
SRL-1: DT 78.0 (14-04-94),
SRL-2: DT 78.1 (05-10-94).

Wet snow cover can be very well identified in the X-SAR images due to low backscattering coefficients. Change detection techniques, based on the X-SAR images from SRL-1 and SRL-2, provide an excellent capability for mapping melting snow areas.

Glacier Studies on the Southern Patagonian Icefield

Glaciological and geodetic measurements have been made on two of the main glaciers, Viedma Glacier and Moreno Glacier, of the Southern Patagonian Icefield which were imaged by SIR-C/X-SAR. Because emphasis of field activities during SRL-1 and SRL-2 was on the test site Ötztal, the campaigns in Patagonia could not be carried out during the shuttle flights. Nevertheless, the information obtained in the field during the campaigns listed below, is of great importance for the analysis of the SIR-C/X-SAR data.

Measurements on Viedma Glacier (22 to 27 Feb. 1994):
- GPS measurements of ground control points along the glacier boundary,
- documentation of surface roughness in the ablation area, including the volcanic ash bands,
- collecting of ash samples and pumice stones from the ash bands on the glacier.
Measurements on Moreno Glacier (1 to 6 March 1994):
- measurement of ice motion and ablation at 4 stakes which had been drilled in Nov. 1993.
Measurements on Moreno Glacier (14 to 30 November 1995):
- drilling of 19 stakes (10 m to 12 m deep) at various locations on the glacier, including a transverse profile (11 stakes) situated 10 km above the glacier terminus,
- measurement of the geodetic position of the stakes by means of differential GPS,
- GPS measurements of ground control points along the glacier boundary,
- installation of an automatic meteorological station at the glacier terminus.

Further field campaigns are planned on Moreno Glacier in March 1996 and November 1996. The planned activities include re-measurement of stakes to determine ice motion and ablation, GPS measurements of glacier boundaries, ice thickness measurements along the transverse profile, echo-sounding of the lake depth in front of the glacier.

Analysis of SIR-C/X-SAR Data:
Emphasis of the analysis so far was on X-SAR data, received in early 1995. In November 1995 we obtained the first SIR-C data (interferometric) of Patagonia. The following data were received:
X-SAR (MGD), Viedma Glacier:
SRL-1: DT 13.06 (10-04-94), DT 25.03 (10-04-94), DT 41.05 (11-04-94), DT 57.05 (12-04-94), DT 73.03 (13-04-94),
SRL-2: DT 09.4 (01-10-94), DT 13.6 (01-10-94), DT 25.3 (01-10-94), DT 45.7 (03-10-94), DT 57.5 (03-10-94), DT 73.3 (04-10-94).
X-SAR (SSC), Moreno Glacier:
SRL-2: DT 121.3 (7-10-94), DT 153.3 (9-10-94), DT 169.3 (10-10-94).
SIR-C (ISLC L-band), Moreno Glacier:
SRL-2: DT 121.3 (7-10-94), DT 153.3 (9-10-94), DT 169.3 (10-10-94).

The boundaries of Viedma Glacier and of the glacier dammed lake Laguna Viedma were mapped from the X-SAR data. Extent and melting conditions of snow and ice areas on the glacier were investigated. Interferometric analysis was carried out for the region of Moreno Glacier, for X-SAR and L-band SIR-C data.

- A major change of the glacier dammed lake Laguna Viedma was found by comparing the X-SAR images from SRL-1 and SRL-2. The lake area decreased from 5.5 km² in April 1994 to 1.5 km² in October 1995 and the water level lowered considerably. This outbreak of the lake, after a long period of comparatively stable glacier position, may indicate changing climatic conditions and the start of a major glacier retreat.

- Good interferograms were obtained on Moreno Glacier from the SIR-C L-band data although the glacier surface was melting. No coherency was obtained over the glacier in the X-SAR data, because backscattering at the shorter wavelengths is more affected by melting. Ice velocities from the L-band interferogram show good agreement with the velocities measured in the field. From the interferogram a map of ice motion can be generated over the whole glacier terminus, most parts of which are inaccessible due to crevasses. Interesting features of the ice motion, including a secondary maximum of velocity just above the calving front, have been identified which had not been known so far.


FUTURE PLANS

- Improvements of target classification and characterization in high Alpine regions, including glaciers and ice-free areas.

- Test of feasibility and accuracy of inversion procedures for snow wetness and for dry snow using the Ötztal data set. The inversion procedures, which have been developed for the SIR-C data of Mammoth by J.C. Shi, will be applied.

- Studies of ice dynamic of Moreno Glacier, based on SIR-C interferometry and on field data. In addition to the campaign in Nov. 1995, the field activities planned for 1996 (ice thickness, motion, glacier boundaries) are of great significance for this task.

- Studies of morphologic characteristics and flow features of Viedma Glacier based on SIR-C and X-SAR data in combination with ERS-1 and ERS-2 SAR data.

- Development of methods for surface shape reconstruction and improvements of digital elevation models, using SIR-C/X-SAR data acquired over the test site Ötztal under various incidence angles and from two look directions (in cooperation with F. Leberl, TU Graz).

Further Data Needs
Innsbruck Region:
SRL-1, SIR-C (MGD): DT 14.2 (10-04-94), DT 46.1 (12-04-94), DT 78.0 (14-04-94),
SRL-2, SIR-C (MGD): DT 14.2 (01-10-94), DT 46.1 (03-10-94), DT 78.1 (05-10-94),
SRL-1, X-SAR (MGD): DT 14.2 (10-04-94), DT 46.1 (12-04-94), (ordered Dec. 28,1995),
SRL-2, X-SAR (MGD): DT 14.2 (01-10-94), DT 46.1 (03-10-94), (ordered Dec. 28,1995).
Moreno Glacier, Patagonia:
SIR-C (C-band ISLC, interferometric), Moreno Glacier:
SRL-2: DT 121.3 (7-10-94), DT 153.3 (9-10-94), DT 169.3 (10-10-94).
Viedma Glacier; Patagonia:
SIR-C (MGD) from SRL-1 and SRL-2, as available.


PUBLICATIONS

Skvarca P., H. Rott and M. Stuefer, 1995: Synergy of ERS-1 SAR, X-SAR, Landsat TM imagery and aerial photography for glaciological studies of Viedma Glacier, southern Patagonia. Proceedings, VII Simposio Latinoamericano de Percepciòn Remota, SELPER, Puerto Vallarta, México, Nov. 1995: 674-682.

Rott H., T. Nagler and D.-M. Floricioiu: Snow and glacier parameters derived from single channel and multi-parameter SAR. Proc. of Int. Symp. on Retrieval of Bio- and Geophysical Parameters from SAR Data for Land Applications , Toulouse, Oct. 1995.

Rott H.: Glacier studies by means of SIR-C/X-SAR. In: The X-SAR Book , W. Noack (Editor).

C. Mätzler, T. Weise, T. Strozzi, D.-M. Floricioiu, H. Rott: Microwave snowpack studies in the Austrian Alps during the SIR-C/X-SAR experiment in April 1994, in preparation.

Rott H., and D.-M. Floricioiu: Analysis of glacier properties with SIR-C/X-SAR. Contribution to the special SIR-C/X-SAR issue of Remote Sensing of Environment, in preparation.

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