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
A high coherence over the maize fields made it possible to create Figures 6 and 7, which give an overview of the final plant heights acquired over the study area
The identification is in accordance with land use classification data of this region (Lussem and Waldhoff, 2014), which was generated using multitemporal optical satellite images and the land use class maize was validated with high accuracy (Waldhoff and Bareth, 2009)
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. 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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