5 research outputs found
Remote sensing applications for monitoring the spatial distribution of Bracken fern (Pteridium) in the Cathedral Peak : Drakensberg, South Africa.
Abstract available in PDF file
Estimating and monitoring land surface phenology in rangelands: A review of progress and challenges
Land surface phenology (LSP) has been extensively explored from global archives of
satellite observations to track and monitor the seasonality of rangeland ecosystems in response
to climate change. Long term monitoring of LSP provides large potential for the evaluation of
interactions and feedbacks between climate and vegetation. With a special focus on the rangeland
ecosystems, the paper reviews the progress, challenges and emerging opportunities in LSP while
identifying possible gaps that could be explored in future. Specifically, the paper traces the evolution
of satellite sensors and interrogates their properties as well as the associated indices and algorithms
in estimating and monitoring LSP in productive rangelands. Findings from the literature revealed
that the spectral characteristics of the early satellite sensors such as Landsat, AVHRR and MODIS
played a critical role in the development of spectral vegetation indices that have been widely used in
LSP applications. The normalized difference vegetation index (NDVI) pioneered LSP investigations,
and most other spectral vegetation indices were primarily developed to address the weaknesses and
shortcomings of the NDVI. New indices continue to be developed based on recent sensors such as
Sentinel-2 that are characterized by unique spectral signatures and fine spatial resolutions, and their
successful usage is catalyzed with the development of cutting-edge algorithms for modeling the
LSP profiles. In this regard, the paper has documented several LSP algorithms that are designed to
provide data smoothing, gap filling and LSP metrics retrieval methods in a single environment
Estimating and monitoring the phenological cycle of bracken fern (Pteridium aquilinum) using remote sensing.
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in PDF
Detection and mapping of bracken fern weeds using multispectral remotely sensed data: a review of progress and challenges
Bracken fern is one of the major invasive plants distributed all over the world currently threatening socio-economic and ecological systems due to its ability to swiftly colonize landscapes. The study aimed at reviewing the progress and challenges in detecting and mapping of bracken fern weeds using different remote sensing techniques. Evidence from literature have revealed that traditional methods such as field surveys and modelling have been insufficient in detecting and mapping the spatial distribution of bracken fern at a regional scale. The applications of medium spatial resolution sensors have been constrained by their limited spatial, spectral and radiometric capabilities in detecting and mapping bracken fern. On the other hand, the availability of most of these data-sets free of charge, large swath width and their high temporal resolution have significantly improved remote sensing of bracken fern. The use of commercial satellite data with high resolution have also proven useful in providing fine spectral and spatial resolution capabilities that are primarily essential to offer precise and reliable data on the spatial distribution of invasive species. However, the application of these data-sets is largely restricted to smaller areas, due to high costs and huge data volumes. Studies on bracken fern classification have extensively adopted traditional classification methods such as supervised maximum likelihood classifier. In studies where traditional methods performed poorly, the combination of soft classifiers such as super resolution analysis and traditional methods of classification have shown an improvement in bracken fern classification. Finally, since high spatial resolution sensors are expensive to acquire and have small swath width, the current study recommends that future research can also consider investigating the utility of the freely available recently launched sensors with a global footprint that has the potential to provide invaluable information for repeated measurement of invasive species over time and space