Quality Assessment for the First Part of the Tandem-X Global Digital Elevation Model

Abstract

ABSTRACT:TanDEM-X is an innovative synthetic aperture radar (SAR) mission with the main goal to generate a global and homogeneous digital elevation model (DEM) of the Earth's land masses. The final DEM product will reach a new dimension of detail with respect to resolution and quality. The absolute horizontal and vertical accuracy shall each be less than 10 m in a 90% confidence interval at a pixel spacing of 12 m. The relative vertical accuracy specification for the TanDEM-X mission foresees a 90% point-to-point error of 2 m (4 m) for areas with predominant terrain slopes smaller than 20% (greater than 20%) within a 1° longitude by 1° latitude cell. The global DEM is derived from interferometric SAR acquisitions performed by two radar satellites flying in close orbit formation. Interferometric performance parameters like the coherence between the two radar images have been monitored and evaluated throughout the mission. In a further step, over 500,000 single SAR scenes are interferometrically processed, calibrated, and mosaicked into a global DEM product which will be completely available in the second half of 2016. This paper presents an up-todate quality status of the single interferometric acquisitions as well as of 50% of the final DEM. The overall DEM quality of these first products promises accuracies well within the specification, especially in terms of absolute height accuracy.

Tandem-X Mission Status

“…Up to now, more than 550,000 Raw DEMs have been generated in a fully automated process employing multibaseline interferometric techniques , Figure 6 the absolute height error (90% confidence level) is depicted for the available final DEM products. The absolute height accuracy measured at global scale is of about 1.2 m, which verifies the outstanding quality of the TanDEM-X DEM (see Table 1) (Bräutigam et al, 2015). Examples of final TanDEM-X DEMs are depicted in Figure 5, 7, and 8.…”

“…Several bistatic experiments were already conducted during the TanDEM-X commissioning phase , (Rodriguez-Cassola et al, 2012), (Lopez-Dekker et al, 2011). To foster the development of further innovative bistatic and multistatic SAR techniques (Cloude et al, 1998), TanDEM-X is operated in a dedicated science phase from October 2014 until December 2015 (Hajnsek, 2015).…”

Wavelet Based Analysis of TanDEM-X and LiDAR DEMs across a Tropical Vegetation Heterogeneity Gradient Driven by Fire Disturbance in Indonesia

“…In the case of TDX DSM WS, scale by scale separability is highest between 4.6 m and 13 m. The reduced separability using TDX DSM WS is related to two main factors: lower spatial resolution of radar compared to LiDAR; difference in information provision of the vertical forest structure due to the lower penetration depth into the canopy (higher attenuation) of TanDEM-X compared to LiDAR in tropical forests [61]. TanDEM-X observations offer the major advantage of global coverage [57] as opposed to a restricted spatial coverage available from airborne LiDAR instruments. Therefore, despite the reduced resolution at the expenses of spatial coverage, 2D wavelet spectra derived from TanDEM-X DSM are still able (to a certain extent) to provide information on vegetation structure.…”

“…Each spectrum sample corresponds to a local wavelet variance estimate at one point in space and for all scales (i.e., a wavelet signature). The interpretation of the wavelet signatures is based on two main considerations: (a) extent to which the The results is key to determine the potential of TanDEM-X DSM for detecting canopy heterogeneity over larger areas compared to airborne LiDAR since TanDEM-X provides global coverage [57]. Moreover, as opposed to a CHM the characterization of canopy heterogeneity does not depend on the availability of ground topography (DTM) but relies on the canopy roughness information provided from a DSM which does not penetrate deep enough into the canopy to reach the ground (in the presence of dense tropical forest) and therefore is restricted to a layer located somewhere within the upper canopy [72].…”

“…The availability of TanDEM-X data has spurred much research on forestry applications and in particular related to vegetation vertical structure (height) through interferometric phase and forest horizontal structure (canopy density) through backscatter and coherence. In this paper we concentrate on the first of these, as a Digital Surface Model (DSM) (WorldDEM TM ) [57] is provided globally so it is the easiest TanDEM-X data product to access and use. Indeed, TanDEM-X provides the first DSM with global coverage, at high resolution (<5 m), which could provide information on canopy heterogeneity.…”