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In this study we show that multiangle remote sensing is useful for increasing the accuracy of vegetation community type mapping in desert regions. Using images from the National Aeronautics and Space Administration (NASA) Multiangle Imaging Spectroradiometer (MISR), we compared roles played by Bidirectional Reflectance Distribution Function (BRDF) model parameters with those played by topographic parameters in improving vegetation community type classifications for the Jornada Experimental Range and the Sevilleta National Wildlife Refuge in New Mexico, USA. The BRDF models used were the Rahman-Pinty-Verstraete (RPV) model and the RossThin-LiSparseReciprocal (RTnLS) model. MISR nadir multispectral reflectance was considered as baseline because nadir observation is the most basic remote sensing observation. The BRDF model parameters and the topographic parameters were considered as additional data. The BRDF model parameters were obtained by inversion of the RPV model and the RTnLS model against the MISR multiangle reflectance data. The results of 32 classification experiments show that the BRDF model parameters are useful for vegetation mapping; they can be used to raise classification accuracies by providing information that is not available in the spectral-nadir domain, or from ancillary topographic parameters. This study suggests that the Moderate Resolution Imaging Spectroradiometer (MODIS) and MISR BRDF model parameter data products have great potential to be used as additional information for vegetation mapping. [ABSTRACT FROM AUTHOR]

Mapping accurately vegetation type is one of the main challenges for monitoring arid and semi-arid grasslands with remote sensing. The multi-angle approach has been demonstrated to be useful for mapping vegetation types in deserts. The current paper presents a study on the use of directional reflectance derived from two sensor systems, using two different models to analyse the data and two different classifiers as a means of mapping vegetation types. The multiangle imaging spectroradiometer (MISR) and the moderate resolution imaging spectroradiometer (MODIS) provide multi-spectral and angular, off-nadir observations. In this study, we demonstrate that reflectance from MISR observations and reflectance anisotropy patterns derived from MODIS observations are capable of working together to increase classification accuracy. The patterns are described by parameters of the modified Rahman-Pinty-Verstraete and the RossThin-LiSparseMODIS bidirectional reflectance distribution function (BRDF) models. The anisotropy patterns derived from MODIS observations are highly complementary to reflectance derived from radiances observed by MISR. Support vector machine algorithms exploit the information carried by the same data sets more effectively than the maximum likelihood classifier. [ABSTRACT FROM AUTHOR]

The goal of the research presented here is to assess the factors controlling the remotely sensed signal returned in the solar wavelengths from Chihuahuan Desert grass-shrub transition canopy-soil complexes. The specific objectives were twofold: to evaluate the importance of the different elements (overstorey, understorey, soil) in the bidirectional reflectance distribution function (BRDF) of a Chihuahuan Desert grass-shrub transition zone; and to explore the behaviour of simple parametric and explicit scattering models with respect to observations. The first objective was approached by simulations using the Radiosity Graphics Method (RGM), with surface parameters provided by measurements of plant locations and dimensions obtained over two contrasting 25 m 2 plots. The second was approached through simulations of bidirectional reflectance factors (BRFs) by both the RGM and a Simplified Geometric Model (SGM) developed for inversion purposes. The modelled BRFs were assessed against multi-angle observations (MAO) - samples of the BRDF at a wavelength of 650 nm acquired from the air at up to six view zenith angles and three solar zenith angles. The results show that the understorey of small forbs and sub-shrubs plays an important role in determining the brightness and reflectance anisotropy of grass-shrub transition landscapes in relation to that of larger shrubs such as mesquite and ephedra. This is owing to the potentially high density of these plants and to the fact that there is also a varying proportion of black grama grass and prone grass litter associated with snakeweed abundance. Both of these components darken the scene. The SGM performed well measured against both the RGM and the MAO at the MAO acquisition angles (R 2 of 0.98 and 0.92, respectively) and good correlations were obtained between RGM and SGM when modelling was performed at a wider range of angular configurations (R 2 ≈0.90). The SGM was shown to be highly sensitive to its adjustable parameters. Both models underestimated BRF magnitude with respect to the MAO by a small amount (<6%), showing increasing divergence from the backscattering into the forward-scattering direction. A remaining problem for operational model inversions using MAO is the a priori estimation of understorey and grass abundance. [ABSTRACT FROM AUTHOR]

This paper assesses the capability of the Roujean and LiSparse-MODIS-RossThin linear semi-empirical kernel-driven (LiSK) bidirectional reflectance distribution function (BRDF) models to predict bidirectional reflectance at geometries other than those of the observations used to invert the model, when the models are inverted against a sparse set of angular samples from 21 orbits (3-19 August 1996) of the operational Advanced Very High Resolution Radiometers (AVHRRs) on NOAA TIROS series AM (morning) and PM (evening) satellites. Red ('visible') and near-infrared (NIR) spectral reflectance estimates acquired at 4:40 GMT on 14 August 1996 by the Along-Track Scanning Radiometer-2 (ATSR-2) sensor flown on the European Space Agency's ERS-2 satellite are used as reference data. The test area is a semi-arid grassland region in Inner Mongolia, P.R. China, bounded by 42.84°-44.71° N and 112.40°-116.05° E. The results show that in spite of the difficulties posed by such a task, LiSK models can be inverted against multiangular AVHRR observations to predict bidirectional reflectance at the acquisition geometry of the ATSR-2 with reasonable accuracy: the rms. error of the reflectance predictions made by both models is less than 4% for the nadir views and less than or equal to 6% in the forward views. These error values are less than one-half those provided by a 13 August 1996 AM AVHRR scene in the 0.65 μm channel and about one-seventh of those for the AVHRR scene in the 0.87 μm (NIR) channel, in both nadir and forward views. [ABSTRACT FROM AUTHOR]

A recent contribution to the Journal suggested that corrections for off-nadir scattering in NOAA-NASA Pathfinder AVHRR Land Data Set may be achieved through polynomial fitting techniques. The method developed is based on assumptions which may not be valid and provides few advantages over the widely-adopted Maximum Value Compositing procedure. While simple and expedient, the polynomial model does not adequately account for the complex surface scattering processes which result in the directional phenomena observed in AVHRR channel 1 and 2 data and does not provide consistent NDVI values. [ABSTRACT FROM AUTHOR]