Salt Content Distribution and Paleoclimatic Significance of the Lop Nur “Ear” Feature: Results from Analysis of EO-1 Hyperion Imagery

Abstract

Lop Nur, a playa lake located on the eastern margin of Tarim Basin in northwestern China, is famous for the "Ear" feature of its salt crust, which appears in remote-sensing images. In this study, partial least squares (PLS) regression was used to estimated Lop Nur playa salt-crust properties, including total salt, Ca , and Fe 2+ using laboratory hyperspectral data. PLS results for laboratory-measured spectra were compared with those for resampled laboratory spectra with the same spectral resolution as Hyperion using the coefficient of determination (R 2 ) and the ratio of standard deviation of sample chemical concentration to root mean squared error (RPD). Based on R 2 and RPD, the results suggest that PLS can predict Ca 2+ using Hyperion reflectance spectra. The Ca 2+ distribution was compared to the "Ear area" shown in a Landsat Thematic Mapper (TM) 5 image. The mean value of reflectance from visible bands for a 14 km transversal profile to the "Ear area" rings was extracted with the TM 5 image. The reflectance was used to build a correlation with Ca 2+ content estimated with PLS using Hyperion. Results show that the correlation between Ca 2+ content and reflectance is in accordance with the evolution of the salt lake. Ca 2+ content variation was consistent with salt deposition. Some areas show a negative correlation between Ca 2+ content and reflectance, indicating that there could have been a small-scale temporary runoff event under an arid environmental background. Further work is needed to determine whether these areas of small-scale runoff are due to natural (climate events) or human factors (upstream channel changes).

Hyperspectral Remote Sensing for Detecting Soil Salinization Using ProSpecTIR-VS Aerial Imagery and Sensor Simulation

“…Despite these factors, the RPD was 2.21, which still indicates the adequacy of the predictive ability of the PLSR model. The reduction in model performance with the scaling up of observations from laboratory to satellite was also observed by Zhang et al [27], after modeling Ca 2+ using Hyperion/EO-1 data in a land degradation area in China. They highlighted the poor SNR of Hyperion as one of the factors that affected the quality of the estimates.…”

“…Such correlation is not observed for all the salts and is typical of the predominance of NaCl. For instance, when treating the soils of the study area with increasing levels of salinization in the laboratory, Moreira et al [27] observed an increase in brightness for NaCl and a decrease in brightness for MgCl 2 and CaCl 2 with increased salt concentration.…”

Modeling and Mapping of Soil Salinity with Reflectance Spectroscopy and Landsat Data Using Two Quantitative Methods (PLSR and MARS)

“…Several studies have shown the visible, near infrared, or short-wave infrared spectral bands from the optical sensors to be promising for the detection of surface soil salinity [11][12][13][14][15]. In addition, hyperspectral data have been successfully used in several studies on soil salinity, enabling quantitative assessment of salt-affected soils [16][17][18][19][20][21][22]. However, practical limitations associated with hyperspectral imagery, including the availability of orbital data and the limited spatial coverage of the existing satellite sensors, still limit its potential for regional monitoring of salt-affected soils [23].…”

Detection and Mapping of Black Rock Coatings Using Hyperion Images: Sudbury, Ontario, Canada

“…Though Hyperion images are characterized by relatively high levels of noise [59,[62][63][64][65][66][67][68], they represent important alternatives to datasets generated by orbiting multispectral systems. In numerous case studies, Hyperion images have proven useful in the mapping of lithological and mineralogical classes [63,64,67,[69][70][71][72][73][74][75][76]. In the Sudbury region, Hyperion images have previously been used in the study of vegetation growth related to land reclamation near smelters [20,77].…”