Lars Boye Hansen

Using remote sensing to assess the protective role of coastal woody vegetation against tsunami waves

This paper describes how remote sensing techniques were used to study the effect of mangroves and other woody coastal vegetation as a protective measure against the 2004 Indian Ocean Tsunami. Remote sensing made it possible to compare pre‐ and post‐Tsunami images of large areas. A study site was selected based on medium resolution Landsat imagery and existing topographic maps. Selection criteria included substantial damages reported, presence of woody vegetated and non‐vegetated shorelines, homogeneous bathymetry and good coverage of pre‐ and post‐Tsunami satellite imagery. The Pichawaram mangrove, Tamil Nadu, India, matched these criteria. Pre‐ and post‐Tsunami Ikonos and QuickBird images were compared through the visual interpretation of pre‐Tsunami coastal vegetation and post‐Tsunami damage. The results were validated in the field. The analysis showed that mangrove forests and coastal shelterbelts provided protection from the Tsunami. This was concluded from analysing the spatial distribution of damage relative to woody vegetation along the coast as well as transects detailing the amount of damage behind the coastline and the coastal woody vegetation.

Documentation and evaluation of the CSE NOAA AVHRR data set

Abstract A NOAA AVHRR data set covering Senegal and parts of the surrounding countries during the period from 1987 to present is under construction and improvement in an ongoing collaboration between Centre de Suivi Écologique (CSE). Dakar. Senegal, and Institute of Geography, University of Copenhagen (IGUC). This paper details the entire processing chain from raw images to a properly calibrated, geometrically rectified and cloud-masked time-series tracking a number of well-defined variables. Two vital aspects of this time series, the cloud masking procedure and the geometrical rectification, are evaluated in detail. A two-step, multi-criteria cloud masking procedure requiring a manual input does not consistently improve the quality of the data set compared to the simpler, automated procedure. With respect to geometrical rectification an accuracy on the order of I km is obtained. Finally, suggestions for further improving the data set are forwarded

Improved calibration of Landsat-5 TM applicable for high-latitude and dark areas

The Landsat-5 Thematic Mapper (TM) has provided data for more than 17 years, making it one of the most successful missions so far. TM sensor degradation is well documented and although efforts are made to account for this degradation when calibrating the sensor, such calibrations are often done over high reflective and bright surfaces in combination with a high solar irradiance. These conditions are not found in high-latitude and dark areas, making the calibration coefficients inappropriate to use. In this study reflectances obtained from TM bands 1–4 over a high-arctic area from 1987–1998 are compared to reflectances obtained from the Landsat-7 Enhanced Thematic Mapper Plus (ETM + ) over the same area in 1999–2000. From the reflectance comparison it was found that a correction of the calibration gain could be described by a power function using days since launch as the controlling variable. From the power function, updated and lifetime calibration coefficients for TM bands 1–4 applicable for high-latitude and dark areas were determined. Furthermore, the study showed a continuous decrease of the TM sensor response with band 1 being the most affected and band 4 the most stable. The study also showed the possibility of using ETM+ to determine updated calibration coefficients for TM by a cross-calibration even though the ETM+ and TM scenes are not coincident.