Invited column-“Hyperspectral remote sensing applications”
2019, 48(3): 303001.
doi: 10.3788/IRLA201948.0303001
With the rapid development of hyperspectral imaging technology, space hyperspectral remote sensing data have been successfully applied to various fields in recent years. The development of space hyperspectral imaging technology at home and abroad was reviewed, the technical standards of representative space hyperspectral imagers were introduced. The latest applications of hyperspectral data in land resources, agriculture and forestry, ocean and lake remote sensing, urban environment, disaster monitoring and other fields in the past five years were systematically summarized and analysed. The outlook of future hyperspectral remote sensing was provided including hyperspectral information extraction and application based on AI technology, the multi-source data fusion and applications, and the analysis and application of hyperspectral data for deep space exploration. Further developments of space hyperspectral imager technology driven by applications will promote the innovated use of hyperspectral data in a wider range of fields.
2019, 48(3): 303002.
doi: 10.3788/IRLA201948.0303002
GF-5 satellite was successfully launched on May 9, 2018. It is the first hyperspectral observation satellite in China. The Greenhouse gas Monitoring Instrument is one of the payloads. It is the first satellite -borne greenhouse gas remote sensing equipment in the world to use spatial heterodyne spectroscopy technology for hyperspectral spectroscopy. The basic working principle of the payload was described, including the principle of light splitting, working mode and band setting. The optical system of the payload consisted of five parts. The core unit was a bonded interferometer. In order to avoid spectral aliasing, the parameters of narrowband filters were required to be high. In order to improve the on-orbit data quantification level, a calibration device based on diffuse reflector system was designed, which can meet the requirements of spectral and radiation calibration. Finally, the basic process of payload data processing was sorted out, and the first batch of observed data was restored by spectrum. The first-level data products are successfully obtained, which lays a foundation for the next application of greenhouse gas inversion.
2019, 48(3): 303003.
doi: 10.3788/IRLA201948.0303003
Compared with traditional multispectral load, the space hyperspectral load has a great improvement in spectral resolution. With the development of quantitative remote sensing, space-based detection can not only collect geometric information of ground targets, but also detect the material composition of atmosphere, land resources, battlefield environment and marine resources by using hyperspectral data. With the continuous development of space hyperspectral technology, it has become possible to monitor global climate, natural resources and hydrographic landforms with high temporal resolution. According to different imaging principles, hyperspectral detection can be divided into interference spectrometer, diffraction spectrometer and filter spectrometer. In this paper, grating diffraction spectrometer, time Fourier transform spectrometer, space Fourier transform spectrometer, AOTF spectrometer, LCTF spectrometer and hyperspectral filter spectrometer were introduced, and the advantages and limitations of each spectrometer were analyzed.
2019, 48(3): 303004.
doi: 10.3788/IRLA201948.0303004
Plateau lakes were of great significance in reflecting changes of regional natural environment under the background of global climate change. Based on the new homemade remote sensing data source, Tiangong-2 multi-spectral data, an automatic extraction algorithm for frozen lake was proposed by used object oriented method combined with water index and elevation information. The algorithm took full account of the characteristics of different forms of water, which can simultaneously extract frozen and unfrozen lakes, and exclude the influence of glaciers and rivers. For the selected 7 typical regions, automatic extraction algorithm was used to carry out lake extraction test and accuracy verification. The overall accuracy of lake extraction is 99.10% and F-score is 0.982. The results show that Tiangong-2 multi-spectral data has a significant application potential in the extraction of plateau lakes. As an effective data source, it can be applied to the study of lake extraction and change in the Tibetan Plateau, and provides data support for the study of regional climate change.
2019, 48(3): 303005.
doi: 10.3788/IRLA201948.0303005
In order to obtain a wide field of view(FOV) and high spatial resolution hyperspectral image while the scanning mirror swinging, the channel separation, FOV and mechanical splicing are required for the geostationary full spectrum hyperspectral imager. If the sub-FOV images are directly spliced, the spectral information of the feature will be distorted because of the different geometric deformation between the sub-FOVs. It was assumed that the difference of the corresponding image points' coordinates between the sub-FOVs was caused by the changes of each sub-FOVs' internal parameters in the paper. A block adjustment method based on the panoramic distortion tangent correction formula was proposed to achieve FOV stitching in the image side coordinate system. The FOV stitching experiment was completed on the basis of four sub-FOVs simulation images in the visible to near-infrared channel, and the stitching accuracy of 0.72 pixels was achieved. The splicing accuracy of the proposed method is close to the block adjustment method's based on the collinear conditional equation. The algorithm is simpler and suitable for primary image production without the assistance of control points and DEM.
2019, 48(3): 303006.
doi: 10.3788/IRLA201948.0303006
The wavelength drift and performance decay of hyper-spectral imager are the main problems that must be solved for long-term operation in orbit. The Fraunhofer absorption line, which is unique in the solar radiation spectrum and the atmospheric backscattering radiation spectrum, can be used as the benchmark for the wavelength calibration. According to the requirement for wavelength calibration precision of instrument, the high precision solar reference spectrum was optimized, then 87 Fraunhofer absorption lines were selected by the convolution of instrument slit function. The system error caused by the line asymmetric and the random error caused by the instrument detection capabilities were analyzed.Based on maximum deviation and RMS, the exact positions for available 76 solar Fraunhofer lines were determined under the condition that the calibration accuracy was better than 0.01 nm. This study lays the foundation for high precision wavelength calibration of hyper-spectral imaging on- orbit.
