Abstract
Abstract. In this study, first results of retrieving plant heights of maize fields from multitemporal TanDEM-X images are shown. Three TanDEM-X dual polarization spotlight acquisitions were taken over a rural area in Germany in the growing season 2014. By interferometric processing, digital terrain models (DTM) were derived for each date with 5m resolution. From the data of the first acquisition (June 1st) taken before planting, a DTM of the bare ground is generated. The data of the following acquisition dates (July 15th, July 26th) are used to establish crop surface models (CSM). A CSM represents the crop surface of a whole field in a high resolution. By subtracting the DTM of the ground from each CSM, the actual plant height is calculated. Within these data sets 30 maize fields in the area of interest could be detected and verified by external land use data. Besides the spaceborne measurements, one of the maize fields was intensively investigated using terrestrial laser scanning (TLS), which was carried out at the same dates as the predicted TanDEM-X acquisitions. Visual inspection of the derived plant heights, and accordance of the individually processed polarisations over the maize fields, demonstrate the feasibility of the proposed method. Unfortunately, the infield variability of the intensively monitored field could not be successfully captured in the TanDEM-X derived plant heights and merely the general trend is visible. Nevertheless, the study shows the potential of the TanDEM-X constellation for maize height monitoring on field level.
Highlights
The TanDEM-X Constellation (TDM) consists of the Synthetic Aperture Radar (SAR) satellites TerraSAR-X and TanDEM-X that fly in a close formation
While the former is taken at the time, where merely the ground of the maize fields was visible, the latter were acquired at the time where the maize plants were developed. This difference can be interpreted as maize plant height at the time of the later acquisitions
The comparison to the terrestrial laser scanning (TLS) measurements revealed an underestimation of the maize plant height derived from TDM and a high standard deviation of the TDM-derived plant heights compared to the TLS-derived plant heights
Summary
The TanDEM-X Constellation (TDM) consists of the Synthetic Aperture Radar (SAR) satellites TerraSAR-X and TanDEM-X that fly in a close formation. TDM is the first satellite based solution for single pass radar interferometry (Krieger et al, 2007). Maize is one of the most important crops in the world. In the context of a growing world population and decreasing area that is available for agriculture, a higher productivity is needed (Spiertz, 2013). Accurate information about the state of maize fields is of great importance to allow precision agriculture techniques. In this context, is has been demonstrated that parameters based on optical and near infrared reflections, such as the Normalized Differenced Vegetation Index (NDVI) correlate with plant height of maize (Freeman et al, 2007). Freeman et al (2007) proposed a combined usage of plant height and NDVI to estimate biomass accumulation, resulting in an improved application of nitrogen
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