TY  - JOUR
A1  - Philipp, Marius B.
A1  - Levick, Shaun R.
T1  - Exploring the potential of C-Band SAR in contributing to burn severity mapping in tropical savanna
JF  - Remote Sensing
N2  - The ability to map burn severity and to understand how it varies as a function of time of year and return frequency is an important tool for landscape management and carbon accounting in tropical savannas. Different indices based on optical satellite imagery are typically used for mapping fire scars and for estimating burn severity. However, cloud cover is a major limitation for analyses using optical data over tropical landscapes. To address this pitfall, we explored the suitability of C-band Synthetic Aperture Radar (SAR) data for detecting vegetation response to fire, using experimental fires in northern Australia. Pre- and post-fire results from Sentinel-1 C-band backscatter intensity data were compared to those of optical satellite imagery and were corroborated against structural changes on the ground that we documented through terrestrial laser scanning (TLS). Sentinel-1 C-band backscatter (VH) proved sensitive to the structural changes imparted by fire and was correlated with the Normalised Burn Ratio (NBR) derived from Sentinel-2 optical data. Our results suggest that C-band SAR holds potential to inform the mapping of burn severity in savannas, but further research is required over larger spatial scales and across a broader spectrum of fire regime conditions before automated products can be developed. Combining both Sentinel-1 SAR and Sentinel-2 multi-spectral data will likely yield the best results for mapping burn severity under a range of weather conditions.
KW  - burn severity
KW  - Sentinel-1
KW  - Sentinel-2
KW  - terrestrial LiDAR
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-193789
SN  - 2072-4292
VL  - 12
IS  - 1
ER  - 
TY  - THES
A1  - Noellie Ahou RUETH, geb. YAO
T1  - Mapping Bushfire Distribution and Burn Severity in West Africa Using Remote Sensing Observations
T1  - Satellitengestützte Kartierung der Verteilung von Buschfeuern und ihrer Auswirkung auf die Vegetation in Westafrika
N2  - Fire has long been considered to be the main ecological factor explaining the origin and maintenance of West African savannas. It has a very high occurrence in these savannas due to high human pressure caused by strong demographic growth and, concomitantly, is used to transform natural savannas into farmland and is also used as a provider of energy. This study was carried out with the support of the BIOTA project funded by the German ministry for Research and Education. The objective of this study is to establish the spatial and temporal distribution of bushfires during a long observation period from 2000 to 2009 as well as to assess fire impact on vegetation through mapping of the burn severity; based on remote sensing and field data collections. Remote sensing was used for this study because of the advantages that it offers in collecting data for long time periods and on different scales. In this case, the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument at 1km resolution is used to assess active fires, and understand the seasonality of fire, its occurrence and its frequency within the vegetation types on a regional scale. Landsat ETM+ imagery at 30 m and field data collections were used to define the characteristics of burn severity related to the biomass loss on a local scale. At a regional scale, the occurrence of fires and rainfall per month correlated very well (R2 = 0.951, r = -0.878, P < 0.01), which shows that the lower the amount of rainfall, the higher the fire occurrence and vice versa. In the dry season, four fire seasons were determined on a regional scale, namely very early fires, which announce the beginning of the fires, early and late fires making up the peak of fire in December/January and very late fires showing the end of the fire season and the beginning of the rainy season. Considerable fire activity was shown to take place in the vegetation zones between the Forest and the Sahel areas. Within these zones, parts of the Sudano-Guinean and the Guinean zones showed a high pixel frequency, i.e. fires occurred in the same place in many years. This high pixel frequency was also found in most protected areas in these zones. As to the kinds of land cover affected by fire, the highest fire occurrence is observed within the Deciduous woodlands and Deciduous shrublands. Concerning the burn severity, which was observed at a local scale, field data correlated closely with the ΔNBR derived from Landsat scenes of Pendjari National Park (R2 = 0.76). The correlation coefficient according to Pearson is r = 0.84 and according to Spearman-Rho, the correlation coefficient is r = 0.86. Very low and low burn severity (with ΔNBR value from 0 to 0.40) affected the vegetation weakly (0-35 percent of biomass loss) whereas moderate and high burn severity greatly affected the vegetation, leading to up to 100 percent of biomass loss, with the ΔNBR value ranging from 0.41 to 0.99. It can be seen from these results that remotely sensed images offer a tool to determine the fire distribution over large regions in savannas and that the Normalised Burn Ratio index can be applied to West Africa savannas. The outcomes of this thesis will hopefully contribute to understanding and, eventually, improving fire regimes in West Africa and their response to climate change and changes in vegetation diversity.
N2  - Feuer ist ein wichtiger ökologischer Faktor für die Biokomplexität und den Fortbestand der westafrikanischen Savannen. Feuer kommt in westafrikanischen Savannen - insbesondere wegen des hohen Bevölkerungsdrucks infolge des starken Bevölkerungswachstums – immer häufiger vor. Es wird sowohl zur Umwandlung natürlicher Savannen in landwirtschaftliche Flächen als auch als Energielieferant verwendet. Diese Studie wurde mit der Unterstützung des BIOTA-Projekts durchgeführt, das vom Bundesministerium für Bildung und Forschung, BMBF, gefördert wird. Ziel dieser Dissertation ist die Bestimmung der räumlichen und zeitlichen Verteilung von Buschfeuern während eines langen Beobachtungszeitraumes (2000-2009) sowie die Kartierung von Brandschäden zum Verständnis der Auswirkung von Feuer auf die lokale Vegetationsstruktur. Fernerkundungs- sowie Felddaten werden in dieser Arbeit verwertet. Fernerkundungsdaten wurden für diese Studie verwendet, da sie größere Flächen abdecken und die Daten über längere Zeiträume in verschiedenen Maßstäben zur Verfügung stehen. Daten des Moderate Resolution Imaging Spectroradiometer (MODIS)-Satelliten mit einer Auflösung von 1 km wurden verwendet, um in regelmäßigen Abständen aktive Feuer zu kartieren und die saisonale Verteilung von Feuern, ihr Vorkommen und ihre Häufigkeit nach Vegetationstyp zu bestimmen. Mit Landsat ETM+ Satellitendaten (Auflösung von 30 Metern) und Felddaten wurden auf einem lokalen Maßstab Brandschadensklassen definiert. Mittels der Biomasse-Felddaten wurde dann der Biomasse-Verlust abgeschätzt. Die Feuerhäufigkeit, mittels Satellitendaten ermittelt, und der Niederschlag pro Monat zeigen eine sehr gute Korrelation (R2 = 0.951, r = -0.878, P < 0.01). Daraus lässt sich schließen, dass Feuer bevorzugt in den Monaten vorkommen, in denen es wenig Niederschlag gibt und umgekehrt. Auf regionaler Ebene wurden innerhalb der Trockenzeit vier Feuer-Perioden identifiziert; ‚sehr frühe Feuer’, die am Anfang der Feuersaison entstehen, ‚frühe bis späte Feuer’, die den Höhepunkt der Feueraktivität im Dezember/Januar bilden, und ‚sehr späte Feuer’ am Ende der Feuersaison bis zum Beginn der Regenzeit. Es zeigte sich, dass eine beträchtliche Feueraktivität in den Vegetationszonen zwischen dem Regenwald und der Sahelzone vorherrscht. Besonders wiesen Teile der ‚Sudan-Guinea’- und der ‚Guinea’-Savanne eine hohe Feuerpixel-Frequenz auf, d.h. hier traten Feuer in vielen Jahren am selben Ort auf. Diese hohe Pixelfrequenz wurde auch in den meisten Schutzgebieten in diesen Savannen-Gebieten gefunden. Was die Landbedeckung betrifft, so ergaben die Ergebnisse, dass das höchste Feueraufkommen in den laubabwerfenden Waldgebieten und im laubabwerfenden Buschland vorkam. Die Brandschäden, bzw. der Einwirkungsgrad, wurden im lokalen Maßstab untersucht. Hier korrelierten die Felddaten zur Brandeinwirkung signifikant mit den sogenannten ΔNBR-Index-Werten, die von Landsat-Aufnahmen des Pendjari-Nationalparks hergeleitet wurden (R2 = 0,76). Der Korrelationskoeffizient nach Pearson ist r = 0,84, und nach Spearman-Rho ist der Koeffizient r = 0,86. Bei sehr niedrigen Brandschäden (mit ΔNBR-Werten zwischen 0 und 0,40) war die Vegetation schwach beeinträchtigt (0-35 % Biomasseverlust), während die Vegetation bei mäßigen und hohen Brandschäden sehr beeinträchtigt war und bis zu 100 % der Biomasse verbrannt war; hier lag der ΔNBR zwischen 0,41 und 0,99. Diese Ergebnisse zeigen, dass durch Satellitenbilder die Verteilung von Feuern über größere Flächen in der afrikanischen Savanne effektiv bestimmt werden kann, und dass der Normalized Burn Ratio-Index auf Westafrika zur Berechnung von Brandschadens-Klassen anwendbar ist. Die Ergebnisse liefern einen entscheidenden Beitrag zum Verständnis von Feuer-Ausprägungen in Westafrika, um letztlich den Einsatz von Feuer, auch im Hinblick auf den Klimawandel und die Veränderungen in der Vegetationsdiversität, verbessern zu können.
KW  - Westafrika
KW  - Fernerkundung
KW  - Feuerökologie
KW  - Vegetation
KW  - Kartierung
KW  - Nationalparks
KW  - Landsat ETM+
KW  - burn severity
KW  - MODIS
KW  - remote sensing
KW  - fire ecology
KW  - fire mapping
KW  - national parks
KW  - vegetation
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-54244
ER  - 
TY  - THES
A1  - Walz, Yvonne
T1  - Measuring burn severity in forests of South-West Western Australia using MODIS
N2  - Burn severity was measured within the Mediterranean sclerophyll forests of south-west Western Australia (WA) using remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The region of south-west WA is considered as a high fire prone landscape and is managed by the state government’s Department of Conservation and Land Management (CALM). Prescribed fuel reduction burning is used as a management tool in this region. The measurement of burn severity with remote sensing data focused on monitoring the success and impact of prescribed burning and wildfire in this environment. The high temporal resolution of MODIS with twice daily overpasses in this area was considered highly favourable, as opportunities for prescribed burning are temporally limited by climatic conditions. The Normalised Burn Ratio (NBR) was investigated to measure burn severity in the forested area of south-west WA. This index has its heritage based on data from the Landsat TM/ETM+ sensors (Key and Benson, 1999 [1],[2]) and was transferred from Landsat to MODIS data. The measurement principally addresses the biomass consumption due to fire, whereas the change detected between the pre-fire image and the post-fire image is quantified by the ÄNBR. The NBR and the Normalised Difference Vegetation Index (NDVI) have been applied to MODIS and Landsat TM/ETM+ data. The spectral properties and the index values of the remote sensing data have been analysed within different burnt areas. The influence of atmospheric and BRDF effects on MODIS data has been investigated by comparing uncorrected top of atmosphere reflectance and atmospheric and BRDF corrected reflectance. The definition of burn severity classes has been established in a field trip to the study area. However, heterogeneous fire behaviour and patchy distribution of different vegetation structure made field classification difficult. Ground truth data has been collected in two different types of vegetation structure present in the burnt area. The burn severity measurement of high resolution Landsat data was assessed based on ground truth data. However, field data was not sufficient for rigorous validation of remote sensing data. The NBR index images of both sensors have been calibrated based on training areas in the high resolution Landsat image. The burn severity classifications of both sensors are comparable, which demonstrates the feasibility of a burn severity measurement using moderate spatial resolution 250m MODIS data. The normalisation through index calculation reduced atmospheric and BRDF effects, and thus MODIS top of at-mosphere data has been considered suitable for the burn severity measurement. The NBR could not be uniformly applied, as different structures of vegetation influenced the range of index values. Furthermore, the index was sensitive to variability in moisture content. However, the study concluded that the NBR on MODIS data is a useful measure of burn severity in the forested area of south-west WA.
KW  - Westaustralien
KW  - Waldbrand
KW  - Fernerkundung
KW  - MODIS
KW  - Waldbraende
KW  - Fernerkundung
KW  - Australien
KW  - MODIS
KW  - mediterranes Oekosystem
KW  - burn severity
KW  - MODIS
KW  - Normalised Burn Ratio (NBR)
KW  - Mediterranean sclerophyll forest
KW  - prescribed burning
Y1  - 2004
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-14745
ER  -