Performances of conventional fusion methods evaluated for inland water body observation using GF-1 image

Satellite remote sensing of inland water body requires a high spatial resolution and a multiband narrow spectral resolution, which makes the fusion between panchromatic(PAN) and multi-spectral(MS) images particularly important. Taking the Daquekou section of the Qiantang River as an observation target, four conventional fusion methods widely accepted in satellite image processing, including pan sharpening(PS), principal component analysis(PCA), Gram-Schmidt(GS), and wavelet fusion(WF), are utilized to fuse MS and PAN images of GF-1.The results of subjective and objective evaluation methods application indicate that GS performs the best,followed by the PCA, the WF and the PS in the order of descending. The existence of a large area of the water body is a dominant factor impacting the fusion performance. Meanwhile, the ability of retaining spatial and spectral informations is an important factor affecting the fusion performance of different fusion methods. The fundamental difference of reflectivity information acquisition between water and land is the reason for the failure of conventional fusion methods for land observation such as the PS to be used in the presence of the large water body. It is suggested that the adoption of the conventional fusion methods in the observing water body as the main target should be taken with caution. The performances of the fusion methods need re-assessment when the large-scale water body is present in the remote sensing image or when the research aims for the water body observation.

An alternative approach to determine critical angle of contrast reversal and surface roughness of oil slicks under sunglint

The critical angle is the angle at which the contrast of oil slicks reverse their contrasts against the surrounding oil-free seawater under sunglint.Accurate determination of the critical angle can help estimate surface roughness and refractive index of the oil slicks.Although it’s difficult to determine a certain critical angle,the potential critical angle range help to improve the estimation accuracy.In this study,the angle between the viewing direction and the direction of mirror reflection is used as an indicator for quantifying the critical angle and could be calculated from the solar/viewing geometry from observations of the Moderate Resolution Imaging Spectroradiometer(MODIS).The natural seep oil slicks in the Gulf of Mexico were first delineated using a customized segmentation approach to remove noise and apply a morphological filter.On the basis of the histograms of the brightness values of the delineated oil slicks,the potential range of the critical angle was determined,and then an optimal critical angle between oil slicks and seawater was then determined from statistical and regression analyses in this range.This critical angle corresponds to the best fitting between the modeled and observed surface roughness of seep oil slicks and seawater.

Data fusion in data scarce areas using a back-propagation artificial neural network model： a case study of the South China Sea

The cloud cover for the South China Sea andits coastal area is relatively large throughout the year,which limits the potential application of optical remotesensing. A H J-charge-coupled device （HJ-CCD） has theadvantages of wide field, high temporal resolution, andshort repeat cycle. However, this instrument suffers fromits use of only four relatively low-quality bands whichcan＇t adequately resolve the features of long wavelengths.The Landsat Enhanced Thematic Mapper-plus （ETM＋）provides high-quality data, however, the Scan LineCorrector （SLC） stopped working and caused striping ofremote sensed images, which dramatically reduced thecoverage of the ETM＋ data. In order to combine theadvantages of the HJ-CCD and Landsat ETM＋ data, weadopted a back-propagation artificial neural network （BP-ANN） to fuse these two data types for this study. Theresults showed that the fused output data not only have theadvantage of data intactness for the HJ-CCD, but also havethe advantages of the multi-spectral and high radiometricresolution of the ETM＋ data. Moreover, the fused datawere analyzed qualitatively, quantitatively and from apractical application point of view. Experimental studiesindicated that the fused data have a full spatial distribution,multi-spectral bands, high radiometric resolution, a smalldifference between the observed and fused output data, anda high correlation between the observed and fused data.The excellent performance in its practical application is afurther demonstration that the fused data are of highquality.