Douglas A. Stow

The relationship between tussock tundra spectral reflectance properties and biomass and vegetation composition

Abstract Frequent cloud cover and logistical constraints hamper biophysical remote sensing studies in arctic locations, resulting in a general lack of information regarding relationships between biophysical quantities and the spectral reflectance of arctic vegetation communities. An experiment was conducted on the north slope of Alaska to characterize relationships between the spectral reflectance of three tussock tundra communities (moist tussock, dry heath and water track) and the above ground biomass and vegetation composition of each community. Hand-held radiometric and ground reference data were collected three times during the 1989 growing season. The normalized difference vegetation index (NDVI) was regressed on above ground photosynthetic and non-photosynthetic biomass quantities and individual blue, green red and near-infrared spectral reflectances and the NDVI were regressed on vegetation cover type fractions. Up to 51 per cent of the variance in the NDVI was explained by the amount of photosynt...

Sensitivity of multitemporal NOAA AVHRR data of an urbanizing region to land-use/land-cover changes and misregistration

Our objectives were to: (1) investigate the sensitivity of multitemporal image data from the Advanced Very High Resolution Radiometer (AVHRR) satellite data for detecting land-use/land-cover changes primarily associated with urbanization and (2) test the effectiveness of a misregistration compensation model on the same data set. Empirical analyses were conducted using two near-anniversary, single-date NOAA AVHHR images of a rapidly urbanizing region of southern and Baja California. Analyses were facilitated by reference data from detailed GIS data layers of land-use/land-cover types for the 2 years corresponding to image acquisition dates (1990 and 1995). Almost all AVHRR pixels containing land-use/land-cover changes were mixed with nonchange areas, even when the extent of change features was greater than the nominal 1 km 2 ground sampling area. The strongest signals of image brightness change were detected by temporal differences of NDVI and Channel 4 surface temperature. ‘‘Undeveloped to urban’’ and ‘‘undeveloped to water’’ were the land-use/land-cover transition sequences with the most definitive AVHRR change signals. Mean magnitudes of misregistration errors were estimated to be around 0.2 pixel units in x and y directions. Mean values for misregistration noise equivalent in brightness change (MNEDB) were 0.02, 0.02, and 1.96 K for image differences of Channel 1 reflectance, NDVI, and Channel 4 surface temperature, respectively. The misregistration compensation model reduced false detection of change, but improvements in detection of land-use/land-cover changes were not conclusive. D 2002 Elsevier

Strategies for Integrating Information from Multiple Spatial Resolutions into Land-Use/Land-Cover Classification Routines

With the development of new remote sensing systems, veryhigh spatial and spectral resolution images now provide a source for detailed and continuous sampling of the Earth’s surface from local to regional scales. This paper presents three strategies for selecting and integrating information from different spatial resolutions into classification routines. One strategy is to combine layers of images of varying resolution. A second strategy involves comparing the a posteriori probabilities of each class at different resolutions. Another strategy is based on a top-down approach starting with the coarsest resolution. The multiresolution strategies are tested using simulated multiresolution images for a portion of the rural-urban fringe of the San Diego Metropolitan Area. The classification accuracy obtained from using three multiple strategies was greater when compared with that from a conventional single-resolution approach. Among the three strategies, the top-down approach resulted in the highest classification accuracy with a Kappa value of 0.648, compared to a Kappa of 0.566 for the conventional classifier.

Connecting the Dots Between Health, Poverty and Place in Accra, Ghana

West Africa has a rapidly growing population, an increasing fraction of which lives in urban informal settlements characterized by inadequate infrastructure and relatively high health risks. Little is known, however, about the spatial or health characteristics of cities in this region or about the spatial inequalities in health within them. In this article we show how we have been creating a data-rich field laboratory in Accra, Ghana, to connect the dots between health, poverty, and place in a large city in West Africa. Our overarching goal is to test the hypothesis that satellite imagery, in combination with census and limited survey data, such as that found in demographic and health surveys (DHSs), can provide clues to the spatial distribution of health inequalities in cities where fewer data exist than those we have collected for Accra. To this end, we have created the first digital boundary file of the city, obtained high spatial resolution satellite imagery for two dates, collected data from a longitudinal panel of 3,200 women spatially distributed throughout Accra, and obtained microlevel data from the census. We have also acquired water, sewerage, and elevation layers and then coupled all of these data with extensive field research on the neighborhood structure of Accra. We show that the proportional abundance of vegetation in a neighborhood serves as a key indicator of local levels of health and well-being and that local perceptions of health risk are not always consistent with objective measures.

Tussock Tundra Albedos on the North Slope of Alaska: Effects of Illumination, Vegetation Composition, and Dust Deposition

Abstract The albedo of tussock tundra was measured at two sites on the north slope of Alaska. One site was selected because of its apparent uniformity and undisturbed condition, while the other site had been visibly affected by dust deposition from the Dalton Highway. Albedo measurements were made under varying cloud-cover conditions. It was hypothesized that observed variations in albedo at the undisturbed site were caused by variations in illumination conditions and ventilation cover type. A simple cloud index (CI) was used to characterize the cloud-cover-illumination conditions, and vegetation cover was described using a hierarchical classification scheme and point-guadrat sampling. Albedo at the undisturbed site was found to be related significantly to variations in CI but unaffected by differences in vegetation cover type. The final component of the study compared the albedo-CI relationships at the undisturbed and dust-impacted sites. It was concluded that dust deposition had a significant direct and...

Land use change detection based on multi-date imagery from different satellite sensor systems

Abstract An empirical study was performed assessing the accuracy of land use change detection when using satellite image data acquired ten years apart by sensors with differing spatial resolutions. Landsat/Multi‐spectral Scanner (MSS) with Landsat/Thematic Mapper (TM) or SPOT/High Resolution Visible (HRV) multi‐spectral (XS) data were used as a multi‐data pair for detecting land use change. The primary objectives of the study were to: (1) compare standard change detection methods (e.g. multi‐date ratioing and principal components analysis) applied to image data of varying spatial resolution; (2) assess whether to transform the raster grid of the higher resolution image data to that of the lower resolution raster grid or vice‐versa in the registration process: and (3) determine if Landsat/TM or SPOT/ HRV(XS) data provides more accurate detection of land use changes when registered to historical Landsat/MSS data. Ratioing multi‐sensor, multi‐date satellite image data produced higher change detection accurac...

Mapping Burn Severity of Mediterranean-Type Vegetation Using Satellite Multispectral Data

Knowledge of the spatial distribution of burn severity immediately following a fire is needed to locate areas requiring management for environmental impacts and timber salvage, and for validation of fire risk and fire behavior models. We evaluated methods for mapping post-fire burn severity in southern California Mediterranean-type ecosystems using satellite images calibrated and validated by field-collected data. The effects of spectral transforms, temporal dimensionality, classifiers, and sensor type on the accuracy of burn severity classification were analyzed. We mapped and analyzed the distributions of five categories of burn severity or land cover for two southern California wildfires based primarily on classification of Landsat TM/ETM+ data, with IKONOS MS data also being evaluated. Map accuracy was assessed relative to field-based classification of burn severity of randomly located plots, using the Composite Burn Index approach. Maps based on the multi-temporal Kauth Thomas transform of Landsat TM/ETM+ data and maximum likelihood classifier had the highest overall accuracy (64 and 55%) and kappa values (0.51 and 0.37) for the two study areas. Forested lands were classified at a much higher level of accuracy (overall accuracy near 80%), while accurate classification of burn severity in shrublands was more challenging (overall accuracy less than 50%). The lower stature vegetation of shrublands typically experiences crown-burning fires, such that range of burn severity for shrublands is more limited.

Satellite-derived vegetation index and cover type maps for estimating carbon dioxide flux for arctic tundra regions

The spatial variability and co-variability of two different types of remote sensing derivatives that portray vegetation and geomorphic patterns are analyzed in the context of estimating regional-scale CO2 flux from land surfaces in the arctic tundra, For a study area encompassing the Kuparuk River watershed of the North Slope of Alaska, we compare satellite-derived maps of the normalized difference vegetation index (NDVI) generated at two different spatial resolutions to a map of vegetation types derived by image classification of data from the Landsat multispectral scanner (MSS). Mean values of NDVI for each cover type stratum are unique (with the exception of moist acidic tundra and shrubland types), Based on analysis of semi-variograms generated for SPOT-NDVI data, most of the vegetation cover and landform features of this arctic tundra landscape have spatial dimensions of less than 1 km. Thaw lakes on the coastal plain and glacial depositional landforms, such as moraines in the foothills, seem to be the largest features, with vegetation units having dimensions no larger than 700 m. Frequency distributions of NDVI and vegetation types extracted for sampling transects flown by an aircraft sensing CO2 flux, relative to distributions for the entire Kuparuk River watershed, suggest a slight sampling bias towards greater cover of mesic wet sedge tundra and thaw lakes and associated lower NDVI values. The regional pattern of NDVI for the North Slope of Alaska corresponds primarily to differences between the two major physiographic provinces of this region

ETHNIC RESIDENTIAL PATTERNS AS PREDICTORS OF INTRA-URBAN CHILD MORTALITY INEQUALITY IN ACCRA, GHANA.

As cities of developing nations absorb an increasing fraction of the worlds population increase, questions have arisen about the potential for emerging inequalities in health within places that are already suffering from inadequate infrastructure. In this paper we explore the pattern of child mortality inequalities (as a proxy for overall health levels) within a large sub-Saharan African city—Accra, Ghana—and then we examine the extent to which existing residential patterns by ethnicity may be predictive of any observed intra-urban inequalities in child mortality. We find that the spatial variability in child mortality in Accra is especially associated with the pattern of residential separation of the Ga from other ethnic groups, with the Ga having higher levels of mortality than other ethnic groups. Being of Ga ethnicity exposes a woman and her children to characteristics of the places in Accra where the Ga live, in which one-room dwellings and poor infrastructure predominate. At the individual level, we find that regardless of where a woman lives, if she is of Ga ethnicity and/or is non-Christian, and if she is not married, her risks of having lost a child are elevated.

Mapping Arctic tundra vegetation types using digital SPOT/HRV-XS data A preliminary assessment

Abstract Multispectral (XS) image data recorded by the High Resolution Visible (HRV) sensor aboard the SPOT-1 satellite are being evaluated for the mapping of Arctic tundra vegetation in the Arctic Foothill Province of Alaska. This research is part of a current ecosystems study that requires an efficient means for mapping vegetation types over large areas. Conventional spectral-based image classification techniques were applied to SPOT/HRV-XS data from a single date. The unique characteristics of the vegetation cover (mainly tussock tundra) and illumination conditions of the location necessitated a detailed examination of classification approaches that have generally been applied in mid-latitude studies. Preliminary results suggest that areal estimates of Arctic tundra vegetation types can be made accurately (±2·5 per cent per category), but maps generated by classifying spectral features of SPOT/HRV-XS data alone arc unsuitably accurate (56 per cent). This is partly due to the high occurrence of relative...