S. Cundill

Detection of hydrocarbons in clay soils: A laboratory experiment using spectroscopy in the mid- and thermal infrared

Remote sensing has been used for direct and indirect detection of hydrocarbons. Most studies so far focused on indirect detection in vegetated areas. We investigated in this research the possibility of detecting hydrocarbons in bare soil through spectral analysis of laboratory samples in the short wave and thermal infrared regions. Soil/oil mixtures were spectrally measured in the laboratory. Analysis of spectra showed development of hydrocarbon absorption features as soils became progressively more contaminated. The future application of these results airborne seems to be a challenge as present and future sensors only cover the diagnostic regions to a limited extent.

Adjusting Spectral Indices for Spectral Response Function Differences of Very High Spatial Resolution Sensors Simulated from Field Spectra

The use of data from multiple sensors is often required to ensure data coverage and continuity, but differences in the spectral characteristics of sensors result in spectral index values being different. This study investigates spectral response function effects on 48 spectral indices for cultivated grasslands using simulated data of 10 very high spatial resolution sensors, convolved from field reflectance spectra of a grass covered dike (with varying vegetation condition). Index values for 48 indices were calculated for original narrow-band spectra and convolved data sets, and then compared. The indices Difference Vegetation Index (DVI), Global Environmental Monitoring Index (GEMI), Enhanced Vegetation Index (EVI), Modified Soil-Adjusted Vegetation Index (MSAVI2) and Soil-Adjusted Vegetation Index (SAVI), which include the difference between the near-infrared and red bands, have values most similar to those of the original spectra across all 10 sensors (1:1 line mean 1:1R2 > 0.960 and linear trend mean ccR2 > 0.997). Additionally, relationships between the indices’ values and two quality indicators for grass covered dikes were compared to those of the original spectra. For the soil moisture indicator, indices that ratio bands performed better across sensors than those that difference bands, while for the dike cover quality indicator, both the choice of bands and their formulation are important.

Investigation of Remote Sensing for Potential Use in Dike Inspection

Dikes are critical barriers against storm surges, sea level rise, and flooding by rivers. Monitoring of these structures is most often done by visual inspection. This paper investigates remote sensing as a tool to facilitate the dike inspection process for grass-covered dikes. Two inspection criteria were considered, namely soil moisture and the quality of the dike cover. Four types of remote sensing data were used, obtained in a ground-based campaign with hand-held sensors. These were thermal, visible, multispectral, and hyperspectral remote sensing data. Relationships were found between the remote sensing data and the inspection criteria. In particular, afternoon thermal remote sensing data showed a negative correlation to soil moisture and broadband multispectral remote sensing data, especially using the near-infrared band, showed a negative correlation to dike cover quality. Limitations for the use of thermal remote sensing are also discussed.

Potential of Using Remote Sensing Data for Dike Inspection

Dikes are increasingly becoming structures of major importance in view of sea level changes. Dike inspectors monitor dikes visually whilst walking the dike. It has been proposed that remote sensing could be used to make dike inspection faster and cheaper. This paper presents the results of a study which investigates remote sensing for evaluating the soil moisture and dike grass cover quality. Correlations were found between soil moisture and thermal and multispectral remote sensing data, and between dike grass cover quality and multispectral remote sensing data. Remote sensing provides useful information for soil moisture and grass cover quality evaluation for dike inspection and may be useful for dike quality inspection.