International Journal of Remote Sensing

Azzarini, F. M.; Pareschi, M. T.; Sbrana, A.; Favalli, M.; Fulignati, P.

doi: 10.1080/01431160118291pmid: N/A

Remotely sensed data (airborne hyperspectral Multispectral Infrared and Visible Imaging Spectroradiometer (MIVIS) data) were used to map active hydrothermal areas at Vulcano island (Sicily), related to a shallow magmatic chamber inducing hot fluid movements in the overlying rocks. A multispectral analysis was carried out using selected MIVIS band combinations and field spectra of selected altered surfaces. Results were checked by field survey, especially in the most active La Fossa crater area, where the zonation of a superficial high sulphidation hydrothermal system was reconstructed. The band selection used was able to clearly discriminate between fresh and hydrothermally altered rocks, especially at La Fossa crater; but differences between advanced argillic and the silicic alteration facies, as identified by field spectra, were not recognized, probably due to the occurrence of fumaroles. Despite the bias introduced by vegetation cover, illumination conditions and buildings, previously unrecognized sites of potential hydrothermal alteration and fumaroles were mapped in the northern sector of Vulcano island.

Russell, R. W.; Wilson, J. W.

doi: 10.1080/01431160118367pmid: N/A

Based on previous radar observations that diurnal 'aerial plankton' (i.e., the ensemble of small, weakly flying insects that drift with the wind ) is usually absent over the ocean, we hypothesized that the insect targets employ flight tactics to resist being drifted overwater. We expected that if aerial insects actively resist overwater drift, then (1) radar-observed clear-air echoes should accumulate along the coastline when winds blow offshore, but they should be advected inland rapidly when winds blow onshore; and (2) accumulations of aerial plankton should be greatest along stretches of coastline most nearly perpendicular to the ambient wind flow. We tested these predictions by comparing the distribution of clear-air radar reflectivity at different sites and under different regimes of wind during the Convection and Precipitation/Electrification (CaPE) Experiment, which was conducted on the east coast of Florida in the summer of 1991. Elevated levels of clearair reflectivity were evident along the coast on mornings when winds were from the west, but not on mornings with easterly winds. On days with westerly winds, this coastal enhancement occurred only in the morning, prior to the onset of the sea breeze. Following sea breeze development, coastal concentrations of clear-air echoes were advected westward and they dispersed rapidly; levels of clear-air reflectivity became depressed overall throughout the study area in the afternoon compared to the morning. Clear-air reflectivity was higher along a north-facing coastline compared to a south-facing coastline when winds had a northward component, with a mirror-image reversal of this pattern on days with southward winds. In contrast, clear-air echoes were uniformly nearly absent from the airspace over the adjacent ocean at all times of the day on all days. These findings support the hypothesis that the organisms comprising the aerial plankton respond behaviourally to coastlines to avoid being blown out to sea. Persistent concentrations of aerial plankton along coastlines may have important consequences for insect population dynamics and local ecosystem structure in coastal regions.

Simms, É.L.; Dubois, J.-M. M.

doi: 10.1080/01431160116919pmid: N/A

Underwater kelp seasonal variation is assessed through the comparative analysis of HRV and Thematic Mapper (TM) images of Baie des Chaleurs between Caps-Noirs and Pointe-Bonaventure, Quebec. The total biomass is estimated, based on the morphology of the dominant species Laminaria longicruris. Kelp-covered and kelp-free areas are differentiated from each other in water depth of 0-6 m and 0-7 m with the HRV and TM images, respectively. The median biomass estimated for the kelp-covered category of the classified image is (1500_400)g m-2. The multidate image shows a spatial variation of the kelp beds in 45% of the area. Areas where no change occurred occupy at least 70 ha, while growth and decay of kelp are observed in much smaller areas, in shallow water and at the boundary of kelp beds.

Sharma, T.; Kiran, P. V. Satya; Singh, T. P.; Trivedi, A. V.; Navalgund, R. R.

doi: 10.1080/01431160117359pmid: N/A

In the arid and semi-arid tropics, low annual rainfall together with high intensity rains has resulted in excess runoff, soil erosion and low moisture intake leading to poor crop yields. Therefore, adoption of soil and water conservation measures is necessary for the optimal utilization of natural resources and to increase the productivity of land on a sustainable basis. Remote sensing and GIS techniques can be used for generating development plans for the watershed area in consonance with the production potential and limitation of terrain resources, and can also be used for assessing the impact of these measures before actual implementation in the field. This paper describes a case study for the Jasdan taluka (district) of Rajkot in Gujarat, India. The aims are to prioritize watersheds on the basis of runoff generated, expressed as yield, due to existing land use conditions; to suggest soil and water conservation measures; and to evaluate the hydrologic response of these measures on runoff. The Soil Conservation Service Curve Number (CN) method was used for computing the runoff; subsequently runoff yield in percentage was calculated for prioritizing the watersheds. Satellite and other collateral data were used to identify the problems and potential in the watersheds and recommend measures for soil and water conservation. The impact of these measures was assessed by computing runoff under alternative land use and management practices. It was found that the runoff yield decreased by 42.88% of the pre-conservation value for the watershed.

McVicar, T. R.; Bierwirth, P. N.

doi: 10.1080/01431160120728pmid: N/A

During 1997 Papua New Guinea (PNG) experienced an intense drought. Emergency famine relief operations provided many subsistence agricultural communities with food, water and health provisions during the height of the drought. The locations of relief operations were based on a rapid and spatially explicit extensive field survey conducted at the height of the drought for all PNG. We have tested the utility of composite Advanced Very High Resolution Radiometer (AVHRR) data to assist in a rapid assessment of drought conditions in PNG. Composited data were used to provide a means to overcome the frequent cloudy conditions that exist in PNG. To assess the drought we divided land surface temperatures (T s) by the Normalized Difference Vegetation Index (NDVI). The ratio (T s/NDVI) increases during times of drought. This is due to the increase in T s associated with more net radiation being partitioned into the sensible heat flux and the decrease in NDVI associated with decreasing amounts of plant cover. A time series of T s/NDVI is a rapid indicator of the drought at the country and province level. We calculated the integral under the T s

Tansey, K. J.; Millington, A. C.

doi: 10.1080/01431160121099pmid: N/A

Multitemporal ERS-1 and ERS-2 SAR data were acquired for northern Jordan between 1995 and 1997 to investigate changes in the backscatter coefficients of a range of typical desert land surfaces. The changes in backscatter found were ascribed to variations in surface soil moisture, and changes in surface roughness caused by a range of natural and anthropogenic factors. Data collected from monitored sites were input into the Integral Equation Model (IEM). The model outputs were strongly correlated with observed backscatter coefficients (r 2=0.84). The results show that the successful monitoring of soil moisture in these environments is strongly dependent on the surface roughness. On surfaces with RMS height 0.5 cm, the sensitivity of the backscatter coefficient to changes in surface microtopography did not allow accurate soil moisture estimation. Microtopographic change on rougher surfaces has less influence on the backscatter coefficient, and the probability of soil moisture estimation from SAR imagery is greater. These results indicate that knowledge of the surface conditions (both in terms of surface roughness and geomorphology) is essential for accurate soil moisture monitoring, whether in a research or operational context. The potential benefits of these findings are discussed in the context of the Jordan Badia Research and Development Project.

Cihlar, J.; Okouneva, G.; Beaubien, J.; Latifovic, R.

doi: 10.1080/01431160118297pmid: N/A

Land cover mapping from multi-spectral satellite data is based primarily on spectral differences in land cover categories. Since only a limited number of cover types are desired in most cases, the images contain redundant information which unnecessarily complicates the digital mapping process. In this study, we have devised an algorithm to automatically and reproducibly quantize an image to be classified into a reduced number of digital levels, in most cases without a visually perceptible reduction in the image information content. The Flexible Histogram Quantization (FHQ) algorithm assumes that the histogram has one or two major peaks (representing water and/or land) and that most of the information of interest is in one peak. It aims to provide a sufficient quantization in the main peak of interest as well as in the tails of this peak by computing an optimized number of quantized levels and then identifying the range of digital values belonging to each level. A comparison of the FHQ with four existing quantization algorithms showed that the FHQ retained substantially more radiometric discrimination than histogram normalization, linear quantization, and scaling methods. Using a random sample of Landsat TM images and an AVHRR coverage of Canada, the average quantization error for the FHQ was 1.68 digital levels for an entire scene and 1.41 for land pixels only. Based on the 34 single-band test images included in the comparison, the radiometric resolution was reduced from 255 to 23.3 levels on the average, or by a factor of 10.94 for a multi-spectral image with n spectral bands. Compared to the other quantization methods, FHQ had a higher efficiency (by 65% to 148%), except for histogram equalization. FHQ also retained more information than histogram equalization (by 11%) but more importantly, it provided finer resolution in the tails of the main histogram peak (by 36-664%, depending on the position in the tails) for infrequent but potentially important land cover types. In addition, unlike the other methods the FHQ does not require a user-specified number of levels and therefore its results are fully reproducible. The F HQ can be used with single scenes, with radiometrically seamless mosaics, or when classifying radiometrically incompatible adjacent scenes. It is concluded that the FHQ provides an effective means for image quantization, as an automated pre-processing step in land cover mapping applications.

Kalluri, S. N. V.; Zhang, Z.; Jájá, J.; Liang, S.; Townshend, J. R. G.

doi: 10.1080/01431160121422pmid: N/A

We used the multi-temporal ten-day composite data from the Advanced Very High Resolution Radiometer (AVHRR) for the years 1983 to 1986 to retrieve the Bidirectional Reflectance Distribution Function (BRDF) using high performance computing techniques. Three different models are used: a simple linear model, a semi-empirical iterative model and a temporal model. The objectives of this study were to compare the performance of different BRDF models at a global scale, assess the computational requirements and optimize the algorithm implementation using high performance computational techniques, and to determine if there is any coherent spatial structure in the coefficients of different BRDF models corresponding to different land cover types. The standard error between model computed reflectances and the input data was used to quantify the performance of the models. Even though the iterative model is computationally more expensive (158 minutes) than either the simple linear model (15 minutes) or the temporal model (16 minutes), the results from all the three models were very similar when the BRDF was estimated at discrete time periods. If the BRDF models were applied without dividing the input data into discrete time intervals, then the temporal model gave better results than the other two. All the models were run on an IBM SP2 parallel machine with 16 CPUs. Most of the mountainous and snow covered areas in high latitudes had null values since the cloud screening algorithm used in the Pathfinder processing performed poorly in distinguishing between snow and clouds. The BRDF coefficients of the iterative model and the Fourier coefficients of the temporal model showed a strong spatial structure corresponding to known variations in land cover.

Ben-Dor, E.; Levin, N.; Saaroni, H.

doi: 10.1080/01431160117759pmid: N/A

Ricchetti, E.

doi: 10.1080/713860801pmid: N/A

Radar-multispectral imagery fusion has been successfully used in several application fields. In this study, a new technique to merge an ERS-1 (Synthetic Aperture Radar precision image, SAR-PRI) image and a Landsat Thematic Mapper (TM ) image for the geological study of the western Aspromonte (southern Italy) was investigated. Spectral information provided by the TM image can be effectively combined with texture and pattern data from the radar imagery to produce a synergistic image. Landsat bands are normalized for shadowing effects using the semi-empirical Minnaert model and thereafter multiplied by the ERS1 image. The visible-infrared (VIR) and radar fused bands can be composed into colour images. This technique leads to the production of images in which the geologically relevant information were integrated. These images were compared with the imagery produced by the intensity-hue-saturation (IHS) transformation approach, commonly used for image fusion. The sun-illumination normalization method gives better results in image fusion, enhancing subtle spectral features. Compared to the individual images, the synergistic SAR-TM images produced by this technique improve the interpretation of lithology boundaries and recognition of structural features.