Tandem Mission Research Articles

Combined use of field observations and SAR interferometry to study ice dynamics and mass balance in Dronning Maud Land, Antarctica

In the region of the Schirmacheroase (71 °S, 12°E) various geodetic and glaciological research activities have been carried out in the last decade. Several times three geodetic-glaciological traverses were undertaken to study ice velocity, accumulation and ablation, and ice surface height changes. Repeated ground surveys show a significant decrease in surface heights by about 15 cm/y for a large blue-ice area. This paper presents the first interferometrically derived ice velocity field of the inland ice close to the Schirmacheroase. The interferometric analysis of the synthetic aperture radar (SAR) data is performed in combination with ground-based information. Since only ERS-1&2 tandem mission image couples are available for this region a digital elevation model (DEM) is used to remove the effect of topography. Ice velocities up to 100 m/y are proved interferometrically for this part of the inland ice.

The motion field of northern Larsen Ice Shelf, Antarctic Peninsula, derived from satellite imagery

AbstractThe motion field of the northern Larsen Ice Shelf, Antarctic Peninsula, was analyzed, based on Landsat data from 1986 to 1989, Earth Resources Satellite (ERS) synthetic aperture radar (SAR) data from 1992 to 1997, and comparative field measurements along three transects. During this period the northern sections of the ice shelf showed steady retreat, which culminated in the disintegration of the two ice-shelf sections north of Seal Nunataks in January 1995. Velocities of these two sections were derived by cross-correlation, using SAR images of 1 year time intervals and Landsat images of 1-3 year intervals. A slight increase of velocity was observed as crevasses and rifts opened before the final disintegration. In addition, an interferometric motion analysis was carried out for the ice shelf around and south of Seal Nunataks, based on an image pair from the ERS-1/2 Tandem Mission in 1995. This analysis reveals a complex pattern of tidal flexure in the grounding zones, as well as rifting and shear zones on the ice shelf. In addition, the motion of the main input glaciers was derived.

Precise orbit determination and gravity field improvement for the ERS satellites

The radial orbit error has long been the major error source in ERS‐1 altimetry, crippled by having only satellite laser ranging for precise tracking and relying on insufficiently accurate general‐purpose gravity field models. Altimeter crossovers are used very effectively as additional tracking data to laser ranging. The ERS Tandem Mission even provides the unique possibility to simultaneously determine orbits of two similar satellites flying the same orbit. Altimeter crossovers between the two satellites then link the two orbits into a common reference frame. Tailoring of the Joint Gravity Model 3 (JGM 3) is another step to reduce orbit errors. This technique is aimed at the reduction of the geographically anticorrelated orbit error (observed in the crossover height differences) through the adjustment of selected gravity field parameters. The resulting Delft Gravity Model (DGM)‐E04 has reduced this part of the orbit error by a factor of 2, performs even better with respect to the ESA‐provided orbits, and also outperforms the recent Earth Geopotential Model EGM96 in this respect. ERS‐1 and ERS‐2 orbits for the entire Tandem Mission are computed and studied in detail, and orbit errors due to the gravity field and nonconservative forces are identified. Analyses systematically show that the orbits computed with JGM 3 have a radial root‐mean‐square orbit accuracy of 7 cm, with DGM‐E04 5 cm.

Demonstration of ERS Tandem Mission SAR Interferometry for Mapping Land Fast Ice Evolution

RÉSUMÉUne série temporelle d'interférogrammes de la mission en tandem d'ERS à partir de paires d'images RSO du chenal de Resolute, Territoires du Nord-Ouest, Canada. Ces images contiennent de l'information sur l'évolution des glaciers terrestres au cours d'une saison et confirme l'évidence du mouvement relatif des glaces le long des fractures.

ERS- [formula omitted] SAR data for the analysis of sedimentary complexes in the matese area (Southern Italy)

This paper deals with the analysis of SAR data acquired during the ESA-ERS tandem mission in order to identify the main morphostructures of the Matese area. These have been inferred by means of power images. Particularly, the structures cutting the Matese massif have apenninic direction and divide it into three great blocks. As well, the images have allowed to identify the outcropping stratigraphic-structural units. Moreover, the ERS tandem mission offers the opportunity to get data useful for repeat-pass SAR interferometry: the 1-day acquisition time interval and the precise orbit control allow to obtain short interferometric baselines and high correlation. Thus, the interferometric fringes so produced are Suitable for morphological analyses.

ERS-1 and ERS-2 tandem mission: Orbit determination, prediction and maintenance

After a short summary of the successful orbit operations during the ERS-2 Launch and Early Orbit Phase, the transition to and implementation of the tandem mission for the two satellites is described, including a comparison of the required and achieved ground track spacing. The new implementation of the routine operational and precise orbit determination and prediction systems is presented briefly, and an estimate of the current orbit prediction and determination accuracy is given. These statistics include tracking data residuals, comparison between routine and precise orbits, comparisons with the D-PAF preliminary orbit solutions, and routine orbit prediction accuracy. Some geophysical results from the altimeter data, obtained in the precise orbit determination, are presented, with special attention to the calibration of the ERS-2 instrument. This paper also introduces the information presented on the Near-Earth Navigation and Geodesy Section's WWW pages on the Internet, where information about the routine and precise orbit determination for ERS-1 and ERS-2 is updated on a daily to weekly basis. Finally, some first results of the ERS-2 PRARE data processing at ESOC are presented.