Papers by Jan G. P. W. Clevers
This paper describes the results of a feasibility study to test the usefulness of MERIS for land ... more This paper describes the results of a feasibility study to test the usefulness of MERIS for land cover mapping. The Netherlands was used as a test site because of its highly fragmented landscape. Results showed that the geometric and radiometric properties of the studied MERIS images of the Netherlands are suitable for land applications. Calculation of principal components and correlation coefficients revealed that the 15 MERIS bands provided a lot of redundant spectral information. For land applications, information came from the visible part of the spectrum on the one hand and from the near-infrared part on the other hand. In addition, the red-edge slope of the reflectance curve (in particular MERIS band 9 at about 708nm) provided supplementary information. The Dutch land use database LGN5 was used as a reference for classifications in this study after aggregation from 25 m to 300 m and recoding to 7 relevant land cover classes. For land cover classification best results in terms of classification accuracies were obtained for the image of 14 July 2003. For the seven land cover classes selected the overall classification accuracy was 67.2%. A multitemporal classification did not improve the overall classification accuracy.
Recent hyperspectral remote sensing allows retrieving the total chlorophyll (C ab) concentration ... more Recent hyperspectral remote sensing allows retrieving the total chlorophyll (C ab) concentration of vegetation using the appropriate optical indices, and/or by means of biochemical information, scaled up from leaf to canopy level within radiative transfer (RT) models. Plenty of chlorophyll optical indices can be found in literature for the leaf level, nevertheless only some of them were proposed for a complex vegetation canopy like a forest stand. A new optical index named Area under curve Normalized to Maximal Band depth between 650-725 nm (ANMB 650-725) is proposed to estimate chlorophyll content of a Norway spruce (Picea abies, Karst.) forest stand. ANMB 650-725 is based on the continuum removal of the chlorophyll absorption feature at the red-edge part of the spectrum between wavelengths of 650-725 nm. Suitability of the index and sensitivity on disturbing factors was tested using a 3D Discrete Anisotropic Radiative Transfer (DART) model coupled with a leaf radiative transfer model PROSPECT adjusted for spruce needles. Results about the ANMB 650-725 abilities within a coniferous forest canopy were compared also with the performance of the chlorophyll indices ratio TCARI/OSAVI. Test results, carried out with the DART model for hyperspectral data with 0.9 m pixel size, showed a strong linear regression of the ANMB 650-725 on spruce crown C ab concentration (R 2 =0.9798) and quite strong resistance against varying canopy structural features such as LAI and canopy closure. The root mean square error (RMSE) between real and the ANMB 650-725 estimated C ab concentrations was only 9.53 μg/cm 2 while the RMSE generated from prediction of the TCARI/OSAVI was two times higher (18.83 μg/cm 2). Chlorophyll retrieval using the ANMB 650-725 index remained stable also after introduction of two signal disturbing features, i/ 20% of the spectral information of epiphytic lichen (Pseudevernia sp.) regularly distributed within the spruce canopy, and ii/ simulation of higher sensor noise (computed for a signal to noise ratio equal to 5).
Recent hyperspectral remote sensing allows retrieving the total chlorophyll (C ab) concentration ... more Recent hyperspectral remote sensing allows retrieving the total chlorophyll (C ab) concentration of vegetation using the appropriate optical indices, and/or by means of biochemical information, scaled up from leaf to canopy level within radiative transfer (RT) models. Plenty of chlorophyll optical indices can be found in literature for the leaf level, nevertheless only some of them were proposed for a complex vegetation canopy like a forest stand. A new optical index named Area under curve Normalized to Maximal Band depth between 650-725 nm (ANMB 650-725) is proposed to estimate chlorophyll content of a Norway spruce (Picea abies, Karst.) forest stand. ANMB 650-725 is based on the continuum removal of the chlorophyll absorption feature at the red-edge part of the spectrum between wavelengths of 650-725 nm. Suitability of the index and sensitivity on disturbing factors was tested using a 3D Discrete Anisotropic Radiative Transfer (DART) model coupled with a leaf radiative transfer model PROSPECT adjusted for spruce needles. Results about the ANMB 650-725 abilities within a coniferous forest canopy were compared also with the performance of the chlorophyll indices ratio TCARI/OSAVI. Test results, carried out with the DART model for hyperspectral data with 0.9 m pixel size, showed a strong linear regression of the ANMB 650-725 on spruce crown C ab concentration (R 2 =0.9798) and quite strong resistance against varying canopy structural features such as LAI and canopy closure. The root mean square error (RMSE) between real and the ANMB 650-725 estimated C ab concentrations was only 9.53 μg/cm 2 while the RMSE generated from prediction of the TCARI/OSAVI was two times higher (18.83 μg/cm 2). Chlorophyll retrieval using the ANMB 650-725 index remained stable also after introduction of two signal disturbing features, i/ 20% of the spectral information of epiphytic lichen (Pseudevernia sp.) regularly distributed within the spruce canopy, and ii/ simulation of higher sensor noise (computed for a signal to noise ratio equal to 5).
Remote Sensing, 2013
The hyper-arid Atacama Desert is one of the most extreme environments for life and only few speci... more The hyper-arid Atacama Desert is one of the most extreme environments for life and only few species have evolved to survive its aridness. One such species is the tree Prosopis tamarugo Phil. Because Tamarugo completely depends on groundwater, it is being threatened by the high water demand from the Chilean mining industry and the human consumption. In this paper, we identified the most important biophysical variables to assess the water status of Tamarugo trees and tested the potential of WorldView2 satellite images to retrieve these variables. We propose green canopy fraction (GCF) and green drip line leaf area index (DLLAI green ) as best variables and a value of 0.25 GCF as a critical threshold for Tamarugo survival. Using the WorldView2 spectral bands and an object-based image analysis, we showed that the NDVI and the Red-edge Chlorophyll Index (CI Red-edge ) have good potential to retrieve GCF and DLLAI green . The NDVI performed best for DLLAI green (RMSE = 0.4) while the CI Red-edge was best for GCF (RMSE = 0.1). However, both indices were affected by Tamarugo leaf movements (leaves avoid facing direct solar radiation at the hottest time of the day). Thus, monitoring systems OPEN ACCESS Remote Sens. 2013, 5 5065 based on these indices should consider the time of the day and the season of the year at which the satellite images are acquired.
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007
The project is designed to build an interdisciplinary research community focusing on hyperspectra... more The project is designed to build an interdisciplinary research community focusing on hyperspectral imaging activities. The core strategy of the network is to create a powerful interdisciplinary synergy between different domains of expertise closely related to hyperspectral imaging activities in Europe, ranging from sensor design and flight operation to data collection, processing, interpretation, and dissemination. Our main goals in this paper are to present the project to the Geoscience and Remote Sensing community and to provide an overview of the planned activities in each sub-activity covered by the network.
Since the launch of MERIS on board of ENVISAT long term activities using vicarious calibration ap... more Since the launch of MERIS on board of ENVISAT long term activities using vicarious calibration approaches have been set in place to monitor potential drifts in the calibration of the radiance products of MERIS. In this paper, a stable and well monitored reference calibration site named Railroad Valley Playa (Nevada, USA) is used to derive the calibration uncertainties of the MERIS FR TOA radiance over time. Subsequently, a linear interpolation of these uncertainties is performed for a set of images covering the whole of the Netherlands (which is used as a validation site). After this, the images over the Netherlands were corrected on the basis of the previously interpolated uncertainties and classified in 9 land use classes using linear spectral unmixing and matched filtering techniques. The classification endmembers were derived from an image-based land use map of the Netherlands (LGN4) after determining the most homogeneous areas for each land use type by means of a standard purity index and a moving window filter to minimize possible adjacency effects. Finally, the impact of the calibration accuracy over the land use classification is assessed by comparing classification results both for corrected and uncorrected images. We conclude that the classification performance may significantly be increased, when taking into account long-term vicarious calibration results.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2014
Optical properties (OPs) of non-flat narrow plant leaves, i.e., coniferous needles, are extensive... more Optical properties (OPs) of non-flat narrow plant leaves, i.e., coniferous needles, are extensively used by the remote sensing community, in particular for calibration and validation of radiative transfer models at leaf and canopy level. Optical measurements of such small living elements are, however, a technical challenge and only few studies attempted so far to investigate and quantify related measurement errors. In this paper we review current methods and developments measuring optical properties of narrow leaves. We discuss measurement shortcomings and knowledge gaps related to a particular case of non-flat nonbifacial coniferous needle leaves, e.g., needles of Norway spruce (Picea abies (L.) Karst.).
Neth J Agr Sci, 1988
ABSTRACT
International Journal of Photogrammetry and Remote Sensing, Feb 28, 1991
Clevers, J.G.P.W., 1991. Application of the WDVI in estimating LAI at the generative stage of bar... more Clevers, J.G.P.W., 1991. Application of the WDVI in estimating LAI at the generative stage of barley. ISPRS J. Photogramm. Remote Sensing, 46: 37-47.
Http Dx Doi Org 10 1080 01431168808954855, May 7, 2007
For monitoring crop growth and development, remote sensing techniques have proved to offer great ... more For monitoring crop growth and development, remote sensing techniques have proved to offer great possibilities. In agricultural field trials a high temporal and spatial resolution are strict requirements. These can be satisfied by using an airborne multispectral photographic (MSP) system. This system and its calibration are described. Results proved the validity of the applied procedure for atmospheric correction and radiometric calibration, resulting in information about crops in field trials with greater precision than by conventional field sampling methods.
Uploads
Papers by Jan G. P. W. Clevers