Remote Sensing of Photosynthetic Parameters

Remote sensing cannot measure photosynthesis directly. However, remote sensing can provide information about parameters directly or indirectly connected to the photosynthetic activity of a plant or a vegetation canopy. Since the launch of the first earth resource satellite in 1972 researchers focused on the relationship between vegetation and its radiometric response. Comparisons of ground measurements and data of the first generations of the Landsat series proved very soon the suitability of the red and near infrared bands of the sensors for vegetation analysis. In the following years, various mathematical combinations of the green, red and near infrared bands, the so called vegetation indices (Bannani et al., 1995) were developed to quantify properties of plant canopies such as biomass, productivity or vigour (Pearson & Miller, 1972; Kauth & Thomas, 1976; Misra et al., 1977; Huete, 1988). However, the low spectral resolution of those sensors was inadequate to derive biochemical properties of vegetation. The development of hyperspectral instruments with a high number of narrow bands first enabled the quantification of pigment concentration and indices related to the photosynthetic capacity of vegetation. While field spectrometers were used to derive pigment concentration of single leaves or small plots of vegetation, the advent of airborne imaging spectrometers such as the compact airborne spectral imager casi, the Airborne Visible/Infrared Imaging Spectrometer AVIRIS or the HyMAPTM Hyperspectral Scanner enabled the monitoring of vegetated canopies and small landscape sections from the 1980s. Since then a new generation of indices was developed considering limitations known from the first generation (Baret et al., 1989; Qi et al., 1994). However, due to the restriction to airborne instruments the acquisition of hyperspectral images was a cost-intensive task. Studies dealing with this kind of sensors assessing biochemical or biophysical plant properties were limited to a relatively small group of scientists and stakeholders. With the advent of space-borne hyperspectral instruments (e.g. the Compact High Resolution Imaging Spectrometer CHRIS (since 2001), the Moderate Resolution Imaging Spectroradiometer MODIS (since 2002) and the Environmental Mapper EnMAP (launch in 2015)) monitoring of biophysical parameters related to photosynthesis becomes increasingly operational. The growing availability as well as the reduced costs for hyperspectral data had a great impact on the numbers of studies and literature dealing with pigment assessment of native and cultivated vegetation canopies on various spatial scales. Vegetation type and species composition strongly affect the derivation of biochemical plant properties and components. Biochemical components (e.g. chlorophyll content) and related