Michael J. Barnsley

First operational BRDF, albedo nadir reflectance products from MODIS

With the launch of NASA’s Terra satellite and the MODerate Resolution Imaging Spectroradiometer (MODIS), operational Bidirectional Reflectance Distribution Function (BRDF) and albedo products are now being made available to the scientific community. The MODIS BRDF/Albedo algorithm makes use of a semiempirical kernel-driven bidirectional reflectance model and multidate, multispectral data to provide global 1-km gridded and tiled products of the land surface every 16 days. These products include directional hemispherical albedo (black-sky albedo), bihemispherical albedo (white-sky albedo), Nadir BRDF-Adjusted surface Reflectances (NBAR), model parameters describing the BRDF, and extensive quality assurance information. The algorithm has been consistently producing albedo and NBAR for the public since July 2000. Initial evaluations indicate a stable BRDF/Albedo Product, where, for example, the spatial and temporal progression of phenological characteristics is easily detected in the NBAR and albedo results. These early beta and provisional products auger well for the routine production of stable MODIS-derived BRDF parameters, nadir reflectances, and albedos for use by the global observation and modeling communities.

The PROBA/CHRIS mission: a low-cost smallsat for hyperspectral multiangle observations of the Earth surface and atmosphere

The European Space Agencys Project for On-Board Autonomy is intended to demonstrate a range of innovations in the design, construction, and operation of small satellites. It carries a number of scientific instruments, the most advanced of which is the Compact High-Resolution Imaging Spectrometer. A typical nadir image is 13 km /spl times/13 km in size and has 18 narrow spectral channels at 17-m spatial resolution. When operated at 34-m spatial resolution, the instrument can capture data in 62, almost contiguous, spectral channels. The platform is highly manoeuvrable: along-track pointing allows a given site to be imaged five times during a single overpass, while across-track pointing ensures that the revisit time for a site of interest is less than a week. This unique combination of spectral and angular sampling provides a rich source of data with which to study environmental processes in the atmosphere and at the Earths surface.

Sampling the surface bidirectional reflectance distribution function (BRDF): 1. Evaluation of current and future satellite sensors

Abstract The Bidirectional Reflectance Distribution Function (BRDF) of earth surface materials contains information relating to their physical structure and composition that cannot be inferred from their spectral properties alone. Knowledge of the BRDF is also critical to the accurate retrieval of earth surface albedo, since the BRDF describes the angular distribution of reflected radiation under given illumination conditions. Although the BRDF cannot be measured directly, it can be estimated using models of surface scattering in conjunction with reflectance data acquired at different viewing and illumination angles. The ability of a satellite sensor to characterise the BRDF of any point on the earths surface is therefore dependent on (i) the range of view angles over which it is able to acquire data, (ii) the orbital characteristics of the satellite on which it is mounted, and (iii) the time period over which the data are recorded. This paper explores the BRDF sampling capabilities of several satellite ...

Distinguishing urban land-use categories in fine spatial resolution land-cover data using a graph-based, structural pattern recognition system

Abstract This paper presents a preliminary test of a graph-based, structural pattern recognition system — known as XRAG (eXtended Relational Attribute Graph) — that might be used to infer broad categories of urban land-use from very fine spatial resolution, remotely-sensed images. XRAG allows the structural properties of, and relations between, discrete land-cover parcels to be analyzed and interpreted. Although the eventual aim is to derive land-use maps directly from remotely-sensed images, this paper employs Ordnance Survey 1:1,250 scale digital map data to provide the initial land-cover information. These data — free from the complex effects of mixed pixels, misclassification, shadowing and occlusion associated with remotely-sensed images — are used to examine the intrinsic separability of several different categories of urban land-use based on the morphological properties of, and the spatial relations between, their component land-cover parcels. In future studies, the system will be tested on real images. The current system also needs to be extended to incorporate graph-searching algorithms and graph-similarity measures, so that it can be used not only to describe the structural differences between sample areas of known land use, but also to infer land use from the spatial pattern of land cover.

Multiangle remote sensing: Past, present and future

Multiangle remote sensing has many new and important applications in the study of the earths land, ocean, and atmosphere. For land studies, multiangle remote sensing samples the bidirectional reflectance distribution function (BRDF) of land surfaces. The modeling and observation of land surface BRDFs has thus been an area of active research for the past decade. The International Forum on BRDF (IFB) was organized in December, 1998, in San Francisco to summarize recent progress in BRDF research, and to identify important future research topics and determine their priorities. This special issue of Remote Sensing Reviews presents a series of summary papers outlined at the IFB that focus on specific BRDF research areas. This paper provides an overview of the special issue by summarizing IFB discussions and individual papers. It also presents five primary courses of action for the BRDF community identified during the IFB. These include (1) identifying a set of key scientific questions to which multiangle remote sensing provides a qualitative and quantitative advances over more traditional approaches, as well as organizing case studies to show the value added by multiangle remote sensing; (2) exploring different inversion techniques, including data fusion and assimilation, to estimate land surface variables that are highly relevant to climate, environmental and ecological studies; (3) continuing the development of simpler BRDF models for analyzing satellite observations; (4) developing a benchmark validation database; and (5) strengthening graduate education program and outreach activities.

A region-based, graph-theoretic data model for the inference of second-order thematic information from remotely-sensed images

A graph-theoretic data model, XRAG (eXtended Relational Attributed Graph), is described. The model and its associated data structure can be used to represent the structural properties (morphological and symbolic) of, and relations (spatial, topological, non-topological, quantitative and symbolic) between, discrete regions identified in a digital remotely-sensed image. The objective in developing this model is to allow second-order thematic information about the scene to be inferred from an analysis of these properties and relations. The paper briefly outlines the application of this model and an associated set of analytical techniques to infer land use from an initial land cover map derived from a digital remotely-sensed image.

On the Separability of Urban Land-Use Categories in Fine Spatial Scale Land-Cover Data Using Structural Pattern Recognition

It has been widely asserted that the morphology of urban areas is a result of the interactions of urban function and urban form. This has led a number of studies to postulate, either explicitly or implicitly, that a mapping exists between the physical form (land cover) of the urban fabric and its corresponding function and activity (land use), although relatively little quantitative evidence has been presented to support this assertion. This paper presents the results of an investigation into the relationship between urban form and urban function using fine spatial scale digital map data. These are used to derive quantitative information on the morphological properties and spatial structure of the buildings present in a series of urban land-use categories identified in two urban areas (Cardiff and Orpington) in the United Kingdom. A statistical separability analysis of these land-use samples suggests that a mapping exists between urban form and function, which, if replicated for other urban areas, would allow urban land use to be inferred from an analysis of the spatial disposition of land-cover parcels, particularly buildings.

Monitoring Urban Land Use by Earth Observation

This paper discuses the use of high resolution spaceborne Earth observation data in studies of the urban environment. Adopting a rigorous, mathematical approach, it introduces the Spatial Re-classification Kernel (SPARK) algorithm; this is appliedto a suburban area in the south-east of London. It also introduces a region-based, structural pattern recognition approach to the same problem through which urban land use might be inferred from an analysis of the morphological properties and structural relations of discrete land cover regions identified in fine spatial resolution images.

Improvements in Aerosol Optical Depth Estimation Using Multiangle CHRIS/PROBA Images

A method has been developed to estimate aerosol optical depth (AOD) over land surfaces using high spatial resolution, hyperspectral, and multiangle Compact High Resolution Imaging Spectrometer (CHRIS)/Project for On Board Autonomy (PROBA) images. The CHRIS instrument is mounted aboard the PROBA satellite and provides up to 62 bands. The PROBA satellite allows pointing to obtain imagery from five different view angles within a short time interval. The method uses inversion of a coupled surface/atmosphere radiative transfer model and includes a general physical model of angular surface reflectance. An iterative process is used to determine the optimum value providing the best fit of the corrected reflectance values for a number of view angles and wavelengths with those provided by the physical model. This method has previously been demonstrated on data from the Advanced Along-Track Scanning Radiometer and is extended here to the spectral and angular sampling of CHRIS/PROBA. The values obtained from these observations are validated using ground-based sun-photometer measurements. Results from 22 image sets show an rms error of 0.11 in AOD at 550 nm, which is reduced to 0.06 after an automatic screening procedure.

Global albedo, BRDF and nadir BRDF-adjusted reflectance products from MODIS

Annual sequences of the first reprocessed albedo, bidirectional reflectance distribution function (BRDF), and nadir BRDF-adjusted surface reflectance (NBAR) products are being evaluated. BRDF model parameters (or weights) are used to compute black sky albedo at local solar noon and white sky albedo and to compute surface reflectance at a common nadir geometry. In addition to these standard resolution albedo, BRDF, and NBAR products, which are provided in the integerized sinusoidal grid projection, the BRDF parameters, black sky albedos (at local solar noon), and white sky albedos are now also being operationally produced in a global geographic projection known as the Climate Modeling Grid (CMG). These are currently available at a 0.25 degree spatial resolution, although there is community interest in a 0.05 degree resolution. In addition to the operational CMGs, coarser 0.5 degree and 1 degree resolution versions of the reprocessed albedo data have also been produced for the ISLSCP-II initiative. The global distribution of these albedos (as they vary throughout the year) are presented, as well as discussions of the most recent evaluations of the quality of the standard products.