5,088 research outputs found
Mapping Chestnut Stands Using Bi-Temporal VHR Data
This study analyzes the potential of very high resolution (VHR) remote sensing images and extended morphological profiles for mapping Chestnut stands on Tenerife Island (Canary Islands, Spain). Regarding their relevance for ecosystem services in the region (cultural and provisioning services) the public sector demand up-to-date information on chestnut and a simple straight-forward approach is presented in this study. We used two VHR WorldView images (March and May 2015) to cover different phenological phases. Moreover, we included spatial information in the classification process by extended morphological profiles (EMPs). Random forest is used for the classification process and we analyzed the impact of the bi-temporal information as well as of the spatial information on the classification accuracies. The detailed accuracy assessment clearly reveals the benefit of bi-temporal VHR WorldView images and spatial information, derived by EMPs, in terms of the mapping accuracy. The bi-temporal classification outperforms or at least performs equally well when compared to the classification accuracies achieved by the mono-temporal data. The inclusion of spatial information by EMPs further increases the classification accuracy by 5% and reduces the quantity and allocation disagreements on the final map. Overall the new proposed classification strategy proves useful for mapping chestnut stands in a heterogeneous and complex landscape, such as the municipality of La Orotava, Tenerife
Infrared astronomical satellite (IRAS) catalogs and atlases. Volume 1: Explanatory supplement
The Infrared Astronomical Satellite (IRAS) was launched on January 26, 1983. During its 300-day mission, IRAS surveyed over 96 pct of the celestial sphere at four infrared wavelengths, centered approximately at 12, 25, 60, and 100 microns. Volume 1 describes the instrument, the mission, and data reduction
Canopy reflectance modeling in a tropical wooded grassland
Geometric/optical canopy reflectance modeling and spatial/spectral pattern recognition are used to study the form and structure of savanna in West Africa. An invertible plant canopy reflectance model is tested for its ability to estimate the amount of woody vegetation cover in areas of sparsely wooded grassland from remotely sensed data. Dry woodlands and wooded grasslands, commonly referred to as savannas, are important ecologically and economically in Africa, and cover approximately forty percent of the continent by some estimates. The Sahelian and Sudanian savanna make up the important and sensitive transition zone between the tropical forests and the arid Saharan region. The depletion of woody cover, used for fodder and fuel in these regions, has become a very severe problem for the people living there. LANDSAT Thematic Mapper (TM) data is used to stratify woodland and wooded grassland into areas of relatively homogeneous canopy cover, and then by applying an invertible forest canopy reflectance model to estimate directly the height and spacing of the trees in the stands. Since height and spacing are proportional to biomass in some cases, a successful application of the segmentation/modeling techniques will allow direct estimation of woody biomass, as well as cover density, over significant areas of these valuable and sensitive ecosystems. Sahelian savanna sites in the Gourma area of Mali being used by the NASA/GIMMS project (Global Inventory Modeling and Monitoring System, at Goddard Space Flight Center), in conjunction with CIPEA/Mali (Centre International pour l'Elevage en Afrique) will be used for testing the canopy model. The model will also be tested in a Sudanian zone crop/woodland area in the Region of Segou, Mali
First Assessment of Mountains on Northwestern Ellesmere Island, Nunavut, as Potential Astronomical Observing Sites
Ellesmere Island, at the most northerly tip of Canada, possesses the highest
mountain peaks within 10 degrees of the pole. The highest is 2616 m, with many
summits over 1000 m, high enough to place them above a stable low-elevation
thermal inversion that persists through winter darkness. Our group has studied
four mountains along the northwestern coast which have the additional benefit
of smooth onshore airflow from the ice-locked Arctic Ocean. We deployed small
robotic site testing stations at three sites, the highest of which is over 1600
m and within 8 degrees of the pole. Basic weather and sky clarity data for over
three years beginning in 2006 are presented here, and compared with available
nearby sea-level data and one manned mid-elevation site. Our results point to
coastal mountain sites experiencing good weather: low median wind speed, high
clear-sky fraction and the expectation of excellent seeing. Some practical
aspects of access to these remote locations and operation and maintenance of
equipment there are also discussed.Comment: 21 pages, 2 tables, 15 figures; accepted for publication in PAS
The application of remote sensing to identify and measure sealed soil and vegetated surfaces in urban environments
Soil is an important non-renewable source. Its protection and allocation is critical to
sustainable development goals. Urban development presents an important drive of soil
loss due to sealing over by buildings, pavements and transport infrastructure.
Monitoring sealed soil surfaces in urban environments is gaining increasing interest
not only for scientific research studies but also for local planning and national
authorities.
The aim of this research was to investigate the extent to which automated classification
methods can detect soil sealing in UK urban environments, by remote sensing. The
objectives include development of object-based classification methods, using two
types of earth observation data, and evaluation by comparison with manual aerial
photo interpretation techniques.
Four sample areas within the city of Cambridge were used for the development of an
object-based classification model. The acquired data was a true-colour aerial
photography (0.125 m resolution) and a QuickBird satellite imagery (2.8 multi-spectral
resolution). The classification scheme included the following land cover classes: sealed
surfaces, vegetated surfaces, trees, bare soil and rail tracks. Shadowed areas were also
identified as an initial class and attempts were made to reclassify them into the actual
land cover type. The accuracy of the thematic maps was determined by comparison
with polygons derived from manual air-photo interpretation; the average overall
accuracy was 84%. The creation of simple binary maps of sealed vs. vegetated surfaces
resulted in a statistically significant accuracy increase to 92%. The integration of
ancillary data (OS MasterMap) into the object-based model did not improve the
performance of the model (overall accuracy of 91%). The use of satellite data in the
object-based model gave an overall accuracy of 80%, a 7% decrease compared to the
aerial photography.
Future investigation will explore whether the integration of elevation data will aid to
discriminate features such as trees from other vegetation types. The use of colour
infrared aerial photography should also be tested. Finally, the application of the object-
based classification model into a different study area would test its transferability
Reduction of time-resolved space-based CCD photometry developed for MOST Fabry Imaging data
The MOST (Microvariability & Oscillations of STars) satellite obtains
ultraprecise photometry from space with high sampling rates and duty cycles.
Astronomical photometry or imaging missions in low Earth orbits, like MOST, are
especially sensitive to scattered light from Earthshine, and all these missions
have a common need to extract target information from voluminous data cubes.
They consist of upwards of hundreds of thousands of two-dimensional CCD frames
(or sub-rasters) containing from hundreds to millions of pixels each, where the
target information, superposed on background and instrumental effects, is
contained only in a subset of pixels (Fabry Images, defocussed images,
mini-spectra). We describe a novel reduction technique for such data cubes:
resolving linear correlations of target and background pixel intensities. This
stepwise multiple linear regression removes only those target variations which
are also detected in the background. The advantage of regression analysis
versus background subtraction is the appropriate scaling, taking into account
that the amount of contamination may differ from pixel to pixel. The
multivariate solution for all pairs of target/background pixels is minimally
invasive of the raw photometry while being very effective in reducing
contamination due to, e.g., stray light. The technique is tested and
demonstrated with both simulated oscillation signals and real MOST photometry.Comment: 16 pages, 23 figure
Sentinel-1 Shadows Used to Quantify Canopy Loss from Selective Logging in Gabon
Selective logging is a major cause of forest degradation in the tropics, but its precise scale, location and timing are not known as wide-area, automated remote sensing methods are not yet available at this scale. This limits the abilities of governments to police illegal logging, or monitor (and thus receive payments for) reductions in degradation. Sentinel-1, a C-band Synthetic Aperture Radar satellite mission with a 12-day repeat time across the tropics, is a promising tool for this due to the known appearance of shadows in images where canopy trees are removed. However, previous work has relied on optical satellite data for calibration and validation, which has inherent uncertainties, leaving unanswered questions about the minimum magnitude and area of canopy loss this method can detect. Here, we use a novel bi-temporal LiDAR dataset in a forest degradation experiment in Gabon to show that canopy gaps as small as 0.02 ha (two 10 m × 10 m pixels) can be detected by Sentinel-1. The accuracy of our algorithm was highest when using a timeseries of 50 images over 20 months and no multilooking. With these parameters, canopy gaps in our study site were detected with a false alarm rate of 6.2%, a missed detection rate of 12.2%, and were assigned disturbance dates that were a good qualitative match to logging records. The presence of geolocation errors and false alarms makes this method unsuitable for confirming individual disturbances. However, we found a linear relationship (r2=0.74) between the area of detected Sentinel-1 shadow and LiDAR-based canopy loss at a scale of 1 hectare. By applying our method to three years’ worth of imagery over Gabon, we produce the first national scale map of small-magnitude canopy cover loss. We estimate a total gross canopy cover loss of 0.31 Mha, or 1.3% of Gabon’s forested area, which is a far larger area of change than shown in currently available forest loss alert systems using Landsat (0.022 Mha) and Sentinel-1 (0.019 Mha). Our results, which are made accessible through Google Earth Engine, suggest that this approach could be used to quantify the magnitude and timing of degradation more widely across tropical forests
Estimating aboveground woody biomass change in Kalahari woodland: combining field, radar, and optical data sets
Maps that accurately quantify aboveground vegetation biomass (AGB) are essential for ecosystem monitoring and conservation. Throughout Namibia, four vegetation change processes are widespread, namely, deforestation, woodland degradation, the encroachment of the herbaceous and grassy layers by woody strata (woody thickening), and woodland regrowth. All of these vegetation change processes affect a range of key ecosystem services, yet their spatial and temporal dynamics and contributions to AGB change remain poorly understood. This study quantifies AGB associated with the different vegetation change processes over an 8-year period, for a region of Kalahari woodland savannah in northern Namibia. Using data from 101 forest inventory plots collected during two field campaigns (2014–2015), we model AGB as a function of the Advanced Land Observing Satellite Phased Array L-band synthetic aperture radar (PALSAR and PALSAR-2) and dry season Landsat vegetation index composites, for two periods (2007 and 2015). Differences in AGB between 2007 and 2015 were assessed and validated using independent data, and changes in AGB for the main vegetation processes are quantified for the whole study area (75,501 km2). We find that woodland degradation and woody thickening contributed a change in AGB of −14.3 and 2.5 Tg over 14% and 3.5% of the study area, respectively. Deforestation and regrowth contributed a smaller portion of AGB change, i.e. −1.9 and 0.2 Tg over 1.3% and 0.2% of the study area, respectively
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