Kris Nackaerts - Academia.edu (original) (raw)
Papers by Kris Nackaerts
Radiotherapy and Oncology, 2014
PE & RS- …, 2001
Forest managers are in constant need of accurate, up-to-date resource information. A first attemp... more Forest managers are in constant need of accurate, up-to-date resource information. A first attempt towards an operational, quantitative, remote-sensing-based change detection system is described. The change information derived from this system can then be used ...
Quaternary Science Reviews, 1999
Since 1990 archaeological research by the Catholic University of Leuven (Belgium) has been carrie... more Since 1990 archaeological research by the Catholic University of Leuven (Belgium) has been carried out at the ancient site of Sagalassos (Ag\ lasun, Burdur province, Southwestern Turkey). At first, research focused on the excavation of the city and the study of the immediate vicinity which provided it with raw materials. The main objective was to obtain a clear picture of the history and development of the city. Since 1993 research has also incorporated a study of the territory of the Roman city, from prehistoric to modern times, in order to understand why the site was selected for settlement, why it developed into a middle-sized town, its economy and subsistence, how it affected and exploited the environment, its decline, and what changes have taken place in the district subsequently. The focus has now shifted towards obtaining a better understanding of the linkages between human and environment systems so that interrelations between the two can be more readily understood. As a result, a number of environmental topics concerning the territory of the Roman city are presently being studied. This territory extended from Lake Burdur in the West to the Aksu canyon in the East, from the Ag\ lasun Dag\ lari in the North to Mt. Kestel in the South. Interdisciplinary research revealed that for the early Neolithic and the Roman period there was a slightly warmer climate, a richer vegetation and more fertile soils for agricultural practice.
Archaeological Computing Newsletter, 1997
Associatie KULeuven. ...
Byzans als Raum. Zu Methoden und Inhalten der historischen Geographie des östlichen Mittelmeeraumes im Mittelalter. Veröffentlichungen der Kommission für die Tabula Imperii Byzantini, 2000
Associatie KULeuven. ...
International Journal of Geographical Information Science, 1999
Visual impact studies often make use of Boolean viewshed maps created by standard functions imple... more Visual impact studies often make use of Boolean viewshed maps created by standard functions implemented in most raster GIS software. The DEM is used in a deterministic way and possible inaccuracies in the DEM are neglected. Monte Carlo simulations of the errors in the digital elevation data (DEM error) can be used to test the effect of the DEM error on the calculated viewshed. Both an explorational and a quantitative method based on binomial statistics are proposed to analyse the impact of the number of simulations on the accuracy ...
SPIE Proceedings, 1999
ABSTRACT Rapid, reliable and objective estimation of Leaf Area Index (LAI) at various scales is o... more ABSTRACT Rapid, reliable and objective estimation of Leaf Area Index (LAI) at various scales is of utmost importance in numerous studies on the Earth's ecosystem. The Licor LAI-2000 Plant Canopy Analyzer (PCA) correlates measured gap fractions to overall LAI by means of the inversion of a radiative transfer model. The PCA's model assumes a random distribution of foliage elements in the stand canopy. However, clumping is observed at different scales in nature. The objectives of this study were, first, the quantification of the LAI measurement error of the PCA due to foliage clumping at stand-level, and second, the derivation of an easily measurable correction factor. For this, foliage elements were simulated in a virtual 3D-space. PCA LAI measurements were simulated by applying the same PCA inversion model onto virtually taken hemispherical photographs resulting in both exact reference LAI values and corresponding PCA measurements. Fractal dimension, quantifying the deviation from a complete random foliage distribution, was tested as a correction factor for PCA measurements. Correction models for PCA measurements were build, based on the measured fractal dimension. A post validation as performed on field data obtained by means of littertraps (reference). A clear relation between fractal dimension and the proportion of underestimation of LAI by the PCA with increasing clumping of foliage was found. Implementation of the regression model resulted in significantly improved LAI measurements.
A new image segmentation algorithm is presented to delineate vegetation-soil-climate complexes ba... more A new image segmentation algorithm is presented to delineate vegetation-soil-climate complexes based on time series analysis. It is based on the assumption that image pixels characterized by similar normalized difference vegetation index (NDVI) time series correspond to regions with similar vegetation-soil-climate properties. Significant differences in NDVI time series indicate therefore differences in vegetation-soil-climate. Ten-daily NDVI values over the period 1998-2003 from SPOT VEGETATION S10 data were analyzed for South-Africa. Analysis consisted of subtracting NDVI values for each observation in the time series between neighboring pixels. The resulting ‘difference ’ vector was transformed using a Fast Fourier Transformation (FFT). The frequency Fourier transforms that indicate the most important periodic components for vegetation dynamics were subsequently analyzed to discriminate natural variability from dissimilar vegetation-soil-climate properties. The relationship betwee...
2014 6th Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS)
This preliminary study shows the potential of highly flexible drones and hyperspectral technology... more This preliminary study shows the potential of highly flexible drones and hyperspectral technology to make detailed chlorophyll maps of an experimental potato field. A novel, innovative hyperspectral frame camera (Rikola Ltd) was employed to gather the spectral information (24 bands) at 5 cm spatial resolution. A first challenge therefore was to setup a dedicated preprocessing chain for the images coming from this novel sensor. Coregistration of the images was successful resulting in an image displacement of only 1–2 pixels. The chlorophyll map created from the Rikola data corresponded well to the field measurements. R2 values of 0.70 were found for a linear relation between the averaged field chlorophyll measurements and the mean of the (R780-R550)/(R780+R550) index calculated for all vegetated Rikola pixels within an experimental potato cultivar plot. These chlorophyll maps which are directly linked to the vegetation status of the crops can be used by the farmer for better management decision making.
... Museum of Central Africa, B-3080 Tervuren, BELÇIKA J. SCHELVIS-Scarab, Wirdumerweg 1, 9917 PA... more ... Museum of Central Africa, B-3080 Tervuren, BELÇIKA J. SCHELVIS-Scarab, Wirdumerweg 1, 9917 PA Wirdum, The Netherlands ... Köyönü ile Sarıkaya yöresindeki kaya çıkıntılarından kireçtaşı örnekleri alınarak, kireçtaşının bozulması ve aşınması konusunda çalışmalar yapmıştır ...
2014 6th Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS), 2014
This preliminary study shows the potential of highly flexible drones and hyperspectral technology... more This preliminary study shows the potential of highly flexible drones and hyperspectral technology to make detailed chlorophyll maps of an experimental potato field. A novel, innovative hyperspectral frame camera (Rikola Ltd) was employed to gather the spectral information (24 bands) at 5 cm spatial resolution. A first challenge therefore was to setup a dedicated preprocessing chain for the images coming from this novel sensor. Coregistration of the images was successful resulting in an image displacement of only 1–2 pixels. The chlorophyll map created from the Rikola data corresponded well to the field measurements. R2 values of 0.70 were found for a linear relation between the averaged field chlorophyll measurements and the mean of the (R780-R550)/(R780+R550) index calculated for all vegetated Rikola pixels within an experimental potato cultivar plot. These chlorophyll maps which are directly linked to the vegetation status of the crops can be used by the farmer for better manageme...
A hyperspectral data cube contains a huge amount of data. For most applications the relevant info... more A hyperspectral data cube contains a huge amount of data. For most applications the relevant information is located within only a few bands. The selection of the relevant bands without loss of essential information is therefore a critical issue. In this project band selection and classification algorithms are developed and validated for precision farming applications, more precisely for the detection of stress symptoms in fruit trees. Experimental test plots are established in apple orchards. The apple trees are put under different types of stress (fungal infection, nutrient stress, aphids and virus). Three times throughout the growing season of 2002 leaves were sampled from both healthy and reference plots and their reflectance was determined. Nearly coincident in time reflectance measurements were performed above the trees. Finally CASI-2 (Compact Airborne Spectrographic Imager, Itres) and SASI (Shortwave Infrared Airborne Spectrographic Sensor, Itres) images were collected at the...
This paper presents the results of the interdisciplinary study of the Hellenistic outer defences ... more This paper presents the results of the interdisciplinary study of the Hellenistic outer defences at the site of Sagalassos. The aim of this study was to analyse the reciprocal relation and intervisibility of a small part of the Hellenistic outer defences, i.e. a fortress and two watchtowers on the mountain tops immediately north and southwest of the city, and the main north and south approaches to the city. This analysis uses a GIS, thus combining archaeology, computer science and geography. Because of the deceptive accuracy of binary viewshed maps, fuzzy viewsheds were calculated. Two types of viewsheds, projective and reflective, were produced. Because of the sensitivity to the positioning of the observation points of the projective viewsheds, it was decided to also calculate reflective viewsheds. Both projective and reflective viewsheds show that the different towers guard a well defined part of the main north and south approaches to the city. It also became clear that the visibi...
Radiotherapy and Oncology, 2014
PE & RS- …, 2001
Forest managers are in constant need of accurate, up-to-date resource information. A first attemp... more Forest managers are in constant need of accurate, up-to-date resource information. A first attempt towards an operational, quantitative, remote-sensing-based change detection system is described. The change information derived from this system can then be used ...
Quaternary Science Reviews, 1999
Since 1990 archaeological research by the Catholic University of Leuven (Belgium) has been carrie... more Since 1990 archaeological research by the Catholic University of Leuven (Belgium) has been carried out at the ancient site of Sagalassos (Ag\ lasun, Burdur province, Southwestern Turkey). At first, research focused on the excavation of the city and the study of the immediate vicinity which provided it with raw materials. The main objective was to obtain a clear picture of the history and development of the city. Since 1993 research has also incorporated a study of the territory of the Roman city, from prehistoric to modern times, in order to understand why the site was selected for settlement, why it developed into a middle-sized town, its economy and subsistence, how it affected and exploited the environment, its decline, and what changes have taken place in the district subsequently. The focus has now shifted towards obtaining a better understanding of the linkages between human and environment systems so that interrelations between the two can be more readily understood. As a result, a number of environmental topics concerning the territory of the Roman city are presently being studied. This territory extended from Lake Burdur in the West to the Aksu canyon in the East, from the Ag\ lasun Dag\ lari in the North to Mt. Kestel in the South. Interdisciplinary research revealed that for the early Neolithic and the Roman period there was a slightly warmer climate, a richer vegetation and more fertile soils for agricultural practice.
Archaeological Computing Newsletter, 1997
Associatie KULeuven. ...
Byzans als Raum. Zu Methoden und Inhalten der historischen Geographie des östlichen Mittelmeeraumes im Mittelalter. Veröffentlichungen der Kommission für die Tabula Imperii Byzantini, 2000
Associatie KULeuven. ...
International Journal of Geographical Information Science, 1999
Visual impact studies often make use of Boolean viewshed maps created by standard functions imple... more Visual impact studies often make use of Boolean viewshed maps created by standard functions implemented in most raster GIS software. The DEM is used in a deterministic way and possible inaccuracies in the DEM are neglected. Monte Carlo simulations of the errors in the digital elevation data (DEM error) can be used to test the effect of the DEM error on the calculated viewshed. Both an explorational and a quantitative method based on binomial statistics are proposed to analyse the impact of the number of simulations on the accuracy ...
SPIE Proceedings, 1999
ABSTRACT Rapid, reliable and objective estimation of Leaf Area Index (LAI) at various scales is o... more ABSTRACT Rapid, reliable and objective estimation of Leaf Area Index (LAI) at various scales is of utmost importance in numerous studies on the Earth's ecosystem. The Licor LAI-2000 Plant Canopy Analyzer (PCA) correlates measured gap fractions to overall LAI by means of the inversion of a radiative transfer model. The PCA's model assumes a random distribution of foliage elements in the stand canopy. However, clumping is observed at different scales in nature. The objectives of this study were, first, the quantification of the LAI measurement error of the PCA due to foliage clumping at stand-level, and second, the derivation of an easily measurable correction factor. For this, foliage elements were simulated in a virtual 3D-space. PCA LAI measurements were simulated by applying the same PCA inversion model onto virtually taken hemispherical photographs resulting in both exact reference LAI values and corresponding PCA measurements. Fractal dimension, quantifying the deviation from a complete random foliage distribution, was tested as a correction factor for PCA measurements. Correction models for PCA measurements were build, based on the measured fractal dimension. A post validation as performed on field data obtained by means of littertraps (reference). A clear relation between fractal dimension and the proportion of underestimation of LAI by the PCA with increasing clumping of foliage was found. Implementation of the regression model resulted in significantly improved LAI measurements.
A new image segmentation algorithm is presented to delineate vegetation-soil-climate complexes ba... more A new image segmentation algorithm is presented to delineate vegetation-soil-climate complexes based on time series analysis. It is based on the assumption that image pixels characterized by similar normalized difference vegetation index (NDVI) time series correspond to regions with similar vegetation-soil-climate properties. Significant differences in NDVI time series indicate therefore differences in vegetation-soil-climate. Ten-daily NDVI values over the period 1998-2003 from SPOT VEGETATION S10 data were analyzed for South-Africa. Analysis consisted of subtracting NDVI values for each observation in the time series between neighboring pixels. The resulting ‘difference ’ vector was transformed using a Fast Fourier Transformation (FFT). The frequency Fourier transforms that indicate the most important periodic components for vegetation dynamics were subsequently analyzed to discriminate natural variability from dissimilar vegetation-soil-climate properties. The relationship betwee...
2014 6th Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS)
This preliminary study shows the potential of highly flexible drones and hyperspectral technology... more This preliminary study shows the potential of highly flexible drones and hyperspectral technology to make detailed chlorophyll maps of an experimental potato field. A novel, innovative hyperspectral frame camera (Rikola Ltd) was employed to gather the spectral information (24 bands) at 5 cm spatial resolution. A first challenge therefore was to setup a dedicated preprocessing chain for the images coming from this novel sensor. Coregistration of the images was successful resulting in an image displacement of only 1–2 pixels. The chlorophyll map created from the Rikola data corresponded well to the field measurements. R2 values of 0.70 were found for a linear relation between the averaged field chlorophyll measurements and the mean of the (R780-R550)/(R780+R550) index calculated for all vegetated Rikola pixels within an experimental potato cultivar plot. These chlorophyll maps which are directly linked to the vegetation status of the crops can be used by the farmer for better management decision making.
... Museum of Central Africa, B-3080 Tervuren, BELÇIKA J. SCHELVIS-Scarab, Wirdumerweg 1, 9917 PA... more ... Museum of Central Africa, B-3080 Tervuren, BELÇIKA J. SCHELVIS-Scarab, Wirdumerweg 1, 9917 PA Wirdum, The Netherlands ... Köyönü ile Sarıkaya yöresindeki kaya çıkıntılarından kireçtaşı örnekleri alınarak, kireçtaşının bozulması ve aşınması konusunda çalışmalar yapmıştır ...
2014 6th Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS), 2014
This preliminary study shows the potential of highly flexible drones and hyperspectral technology... more This preliminary study shows the potential of highly flexible drones and hyperspectral technology to make detailed chlorophyll maps of an experimental potato field. A novel, innovative hyperspectral frame camera (Rikola Ltd) was employed to gather the spectral information (24 bands) at 5 cm spatial resolution. A first challenge therefore was to setup a dedicated preprocessing chain for the images coming from this novel sensor. Coregistration of the images was successful resulting in an image displacement of only 1–2 pixels. The chlorophyll map created from the Rikola data corresponded well to the field measurements. R2 values of 0.70 were found for a linear relation between the averaged field chlorophyll measurements and the mean of the (R780-R550)/(R780+R550) index calculated for all vegetated Rikola pixels within an experimental potato cultivar plot. These chlorophyll maps which are directly linked to the vegetation status of the crops can be used by the farmer for better manageme...
A hyperspectral data cube contains a huge amount of data. For most applications the relevant info... more A hyperspectral data cube contains a huge amount of data. For most applications the relevant information is located within only a few bands. The selection of the relevant bands without loss of essential information is therefore a critical issue. In this project band selection and classification algorithms are developed and validated for precision farming applications, more precisely for the detection of stress symptoms in fruit trees. Experimental test plots are established in apple orchards. The apple trees are put under different types of stress (fungal infection, nutrient stress, aphids and virus). Three times throughout the growing season of 2002 leaves were sampled from both healthy and reference plots and their reflectance was determined. Nearly coincident in time reflectance measurements were performed above the trees. Finally CASI-2 (Compact Airborne Spectrographic Imager, Itres) and SASI (Shortwave Infrared Airborne Spectrographic Sensor, Itres) images were collected at the...
This paper presents the results of the interdisciplinary study of the Hellenistic outer defences ... more This paper presents the results of the interdisciplinary study of the Hellenistic outer defences at the site of Sagalassos. The aim of this study was to analyse the reciprocal relation and intervisibility of a small part of the Hellenistic outer defences, i.e. a fortress and two watchtowers on the mountain tops immediately north and southwest of the city, and the main north and south approaches to the city. This analysis uses a GIS, thus combining archaeology, computer science and geography. Because of the deceptive accuracy of binary viewshed maps, fuzzy viewsheds were calculated. Two types of viewsheds, projective and reflective, were produced. Because of the sensitivity to the positioning of the observation points of the projective viewsheds, it was decided to also calculate reflective viewsheds. Both projective and reflective viewsheds show that the different towers guard a well defined part of the main north and south approaches to the city. It also became clear that the visibi...