Tobias Kellenberger

Rapid disintegration of Alpine glaciers observed with satellite data

Analyses of multispectral satellite data indicate accelerated glacier decline around the globe since the 1980s. By using digitized glacier outlines inferred from the 1973 inventory and Landsat Thematic Mapper (TM) satellite data from 1985 to 1999, we obtained area changes of about 930 Alpine glaciers. The 18% area reduction as observed for the period 1985 to 1999 (−1.3% a⁻¹) corresponds to a seven times higher loss rate compared to the 1850–1973 decadal mean. Extrapolation of area change rates and cumulative mass balances to all Alpine glaciers yields a corresponding volume loss of about 25 km³ since 1973. Highly individual and non-uniform changes in glacier geometry (disintegration) indicate a massive down-wasting rather than a dynamic response to a changed climate. Our results imply stronger ongoing glacier retreat than assumed so far and a probable further enhancement of glacier disintegration by positive feedbacks.

Radiometric corrections of topographically induced effects on Landsat TM data in an alpine environment

Abstract Four radiometric correction methods for the reduction of slope-aspect effects in a Landsat TM data set are tested in a mountainous test site with regard to their physical soundness and their influence on forest classification, as well as on the visual appearance of the scene. Excellent ground reference information and fine-resolution DEM allowed precise assessment of the applicability of the methods under investigation. The results of the study presented here demonstrate the weakness of the classical cosine correction method for radiometric correction in rugged terrain. The statistical, Minnaert and C-correction approaches, however, yielded an improvement of the forest classification and an impressive reduction of the visual topography effect.

APEX - the hyperspectral ESA Airborne Prism Experiment

The airborne ESA-APEX (Airborne Prism Experiment) hyperspectral mission simulator is described with its distinct specifications to provide high quality remote sensing data. The concept of an automatic calibration, performed in the Calibration Home Base (CHB) by using the Control Test Master (CTM), the In-Flight Calibration facility (IFC), quality flagging (QF) and specific processing in a dedicated Processing and Archiving Facility (PAF), and vicarious calibration experiments are presented. A preview on major applications and the corresponding development efforts to provide scientific data products up to level 2/3 to the user is presented for limnology, vegetation, aerosols, general classification routines and rapid mapping tasks. BRDF (Bidirectional Reflectance Distribution Function) issues are discussed and the spectral database SPECCHIO (Spectral Input/Output) introduced. The optical performance as well as the dedicated software utilities make APEX a state-of-the-art hyperspectral sensor, capable of (a) satisfying the needs of several research communities and (b) helping the understanding of the Earths complex mechanisms.

Mapping urban and peri-urban agriculture using high spatial resolution satellite data

In rapidly changing peri-urban environments where biophysical and socio-economic processes lead to spatial fragmentation of agricultural land, remote sensing offers an efficient tool to collect land cover/land use (LCLU) data for decision-making. Compared to traditional pixel-based approaches, remote sensing with object-based classification methods is reported to achieve improved classification results in complex heterogeneous landscapes. This study assessed the usefulness of object-oriented analysis of Quickbird high spatial resolution satellite data to classify urban and peri-urban agriculture in a limited peri-urban area of Hanoi, Vietnam. The results revealed that segmentation was essential in developing the object-oriented classification approach. Accurate segmentation of shape and size of an object enhanced classification with spectral, textural, morphological, and topological features. A qualitative, visual comparison of the classification results showed successful localisation and identification of most LCLU classes. Quantitative evaluation was conducted with a classification error matrix reaching an overall accuracy of 67% and a kappa coefficient of 0.61. In general, object-oriented classification of high spatial resolution satellite data proved the promising approach for LCLU analysis at village level. Capturing small-scale urban and peri-urban agricultural diversity offers a considerable potential for environmental monitoring. Challenges remain with the delineation of field boundaries and LCLU diversity on more spatially extensive datasets.

3D Modelling with National Coverage: Bridging the Gap Between Research and Practice

3D technologies are becoming mature and more and more organisations are investing in 3D models for their areas. For National Mapping and Cadastral Agencies (NMCAs), that have a long history in collating and maintaining countrywide 2D-datasets, the major challenge is how to best adopt a 2D base into 3D environment with an established process of continuous incremental update, and making best use of available resources. To identify best and common practices, as well as remaining research challenges, since 2013 ten NMCAs work together in the European Spatial Data Research (EuroSDR) 3D Special Interest Group. This paper reports about an inventory that has been made on the state-of-the art of 3D products and plans that these NMCAs have as well as the challenges they face. The 3D modelling of buildings is explored in more detail, since buildings are prominent features in 3D city and landscape models. In addition, together with road objects (traffic infrastructure), building objects change often and therefore these require efficient update processes.

Mapping diversified peri-urban agriculture – potential of object-based versus per-field land cover/land use classification

High spatial resolution satellite data contribute to improving land cover/land use (LCLU) classification in agriculture. A classification procedure based on Quickbird satellite image data was developed to map LCLU of diversified agriculture at sub-communal and communal level (7 km2). Segmentation performance of the panchromatic band in combination with high pass filters (HPF) was tested first. Accuracy of field boundary delineation was evaluated by an object-based segmentation, a per-field and a manual classification, along with a quantitative accuracy assessment. Sub-communal classification revealed an overall accuracy of 84% with a κ coefficient of 0.77 for the per-field vector segmentation compared to an overall accuracy of 56–60% and a κ coefficient of 0.37–0.42 for object-based approaches. Per-field vector segmentation was thus superior and used for LCLU classification at communal level. Overall accuracy scored 83% and the κ coefficient 0.7. In diversified agriculture, per-field vector segmentation and classification achieved higher classification results.

Comparison of different approaches of selecting endmembers to classify agricultural land by means of hyperspectral data (DAIS7915)

A major problem in classification of hyperspectral datasets is the reliable selection of reference spectra to classify heterogeneous vegetated areas. In this work, different approaches of end-member collection for spectral unmixing of hyperspectral data are presented, evaluated and compared to each other. The selected methods include high resolution ground spectroradiometric measurements, a scene based approach and modelling of the end-member spectra using a SVAT (soil-vegetation-atmosphere-transfer) approach. The presented methods are discussed and verified with an extensive ground truth collected in the observed area.

The Swiss field-goniometer system (FIGOS)

The reflectance characteristics of most natural objects vary with illumination and viewing geometry, i.e. expose a non-Lambertian behaviour. New sensor systems are capable of viewing targets quasi-simultaneously from nadir and different off-nadir positions. In regard to radiometric corrections the Lambertian assumption has to be overcome by detailed knowledge of the bidirectional reflectance distribution function (BRDF) of targets at the Earths surface. In order to obtain bidirectional reflectance factor (BRF) data of naturally illuminated targets a transportable field-goniometer system (FIGOS) has been developed. It is operated together with a GER-3700 spectroradiometer. The goniometer consists of an azimuth full-circle and a zenith semi-arc of 2 m radius each. It enables one to observe a target from any desired viewing direction. First measurements are taken from a plane meadow under different solar zenith angles over the hemisphere in a resolution of 15/spl deg/ and 30/spl deg/ in zenith and azimuth direction, respectively. A Spectralon panel is measured at the beginning and end of a hemispherical data set. As the position of the Sun and the atmospheric conditions cannot be assumed constant over the measurement period of about 18 minutes, the global solar irradiance is monitored simultaneously to the BRF-data acquisition. The obtained results clearly show the non-Lambertian reflectance characteristics of the meadow.

Development Of Processing Chains For Rapid Mapping With Satellite Data

In case of a disaster on a large scale the International Charter of Space and Major Disasters (Charter) provides satellite data from different sensors. Since 2000 more than 140 Charter Calls have proven the great value of this fast disaster response instrument but have also shown different handling problems causing time delay and downgrading the value of rapid mapping products. This paper proposes a framework for a rapid mapping processing chain based on the experiences gathered during the 2005 flood crisis in Switzerland. It focuses on the pre-processing of satellite data, the value-adding step and the visualization of the results. Critical elements are hereby the availability of essential datasets, the processing time, the information extraction and the usability of the products for the end-users. International programs containing rapid mapping elements as PREVIEW or GMES RESPOND and RISK-EOS need further research on the abovementioned topics to improve the usability and significance of their products and to improve the benefit of satellite data for disaster management support.

Aspects of atmospheric and topographic correction of high spatial resolution imagery

The new method for cast shadow detection has shown to significantly improve the topographic image correction. This method will be used for operational processing of remote sensing products based on the ADS systems operated by the Swiss Federal Institute of Topography (swisstopo) and will be available in future releases of the ATCOR software packages.