Interferometric Digital Elevation Model Generation Using ICEYE Data

High resolution, digital representation of surface topography and surface features is key to understanding global changes of terrain due to natural phenomena but also due to manmade changes. Digital Elevation Models (DEMs) can be retrieved from various methods such as SAR Interferometry (InSAR), Photogrammetry or Lidar systems using satellite or aerial data . 

SAR data has the unique advantage that both amplitude and phase are recorded by the SAR antenna. The phase information, which determines the distance from the sensor to a target, is essential for interferometric DEM generation. In comparison to e.g. radargrammetric methods, more accurate DEM results can be derived. Hence, spaceborne SAR interferometry has developed as a key method to derive digital elevation models. The first near global dataset has been presented by the Shuttle Radar Topography Mission in 2000 and since then has been complemented by ESA’s global Copernicus DEM derived from the bistatic TanDEM-X mission . However, other currently commercially available spaceborne SAR systems are not suitable for interferometric DEM generation due to constraints arising from both  normal and temporal baselines between image acquisitions. 

ICEYE has launched 31 satellites up to date (as of December 2023) and operates the largest spaceborne SAR constellation currently available. The fleet of satellites allows for tasking of pursuit monostatic image pairs where both satellites fly in an identical satellite orbit with a short temporal separation. Both satellites individually transmit and receive their own radar pulse. Suitable imaging geometries , i.e., long enough normal baselines and short enough temporal baselines, allow for InSAR derived DEM generation. Pursuit monostatic image pairs with short temporal baselines are hardly affected by atmospheric delay, similarly to bistatic formations, however, as both satellites operate as individual systems, image acquisition and processing is simpler than for bistatic formation flying.

In this study we present 1) results from interferometric DEM generation using high resolution ICEYE SAR data and 2) a quality assessment of the derived pursuit monostatic DEMs. Resulting DEMs have been derived for different study sites using pursuit monostatic image pairs with short temporal baselines acquired in Strip or Spot imaging modes. The suitability of various baseline settings has been tested and limiting baselines determined. A vertical accuracy assessment has been performed against external datasets such as airborne LiDAR derived DEMs or NASA’s ICESat-2 ATL08 Terrain points  (https://nsidc.org/data/atl08/versions/6).

The results show high spatial detail of surface topography with a DEM resolution finer than 3 m for Spot and 5 m for Strip imaging modes. The vertical accuracy has proven to be better than 3 m RMSE in open and relatively flat areas (slopes less than 10 degrees) when compared to external datasets. Yet, interferometric processing has shown to be challenging when affected by temporal decorrelation between image acquisitions, vegetation coverage or steep terrain.