Assessment of NDVI- Differences Caused by Sensor Specific Relative Spectral Response Functions

The normalized difference vegetation index (NDVI) is the most often used remote sensing-based indicator to monitor dynamics of land surfaces and environmental changes. Due to different sensor characteristics, the NDVI values vary according to the recording system. This study focuses on the factor of spectral sensor characteristics, which can complicate the interpretation of multisensoral NDVI data. Therefore, multispectral bands of Landsat 5TM, QuickBird and SPOT5 were simulated from hyperspectral data. These simulated data sets show identical characteristics (except spectrally) like sensor geometry, atmospheric conditions, topography and spatial resolution. This allows a direct comparison of NDVI differences caused by the factor of different spectral characteristics. The results show substantial NDVI differences with a systematic nonlinear offset between the sensor systems, solely caused by different relative spectral response functions of the sensor bands. Thus, a step-by-step sensor intercalibration is desirable, which first takes the spectral characteristics into account, because this NDVI-differences causing factor is clearly determinable against others.