Interference Imaging Spectrometer Research Articles

Mapping the spatial distributions of oxide abundances and Mg# on the lunar surface using multi-source data and a new ensemble learning algorithm

The spatial distribution of oxide abundances and Mg# (Mg/(Mg + Fe)) on the lunar surface is of great significance for understanding the origin and evolution of the Moon. China’s Chang’E-5 (CE-5) mission returned young lunar soils for the first time, providing a new ground truth for the inversion of oxide abundances. In this study, the relationship between multi-source remote sensing data (including Chang’E-1 Interference Imaging Spectrometer (CE-1 IIM) data and the new global Christiansen feature (CF) product, named IIM-CF data), and the abundances of six oxides (FeO, TiO2, MgO, SiO2, Al2O3 and CaO) measured at 40 lunar sampling sites including CE-5 were analyzed. The use of IIM-CF data as the input features of the selected inversion models for obtaining the abundances of oxides, and the oxide abundances measured at the 40 sampling sites were used as the ground truth of the oxide abundances. The models selected for investigation contain three common algorithms − random forest (RF), extreme gradient boosting (XGBoost) and partial least squares regression (PLSR), and a new method integrates RF, XGBoost and PLSR together named RXP was developed in this study. The modeling results of the abundances of the six oxides derived from the above four algorithms show that the RXP algorithm outperforms the other three algorithms. The distributions of the six oxides and Mg# on the lunar surface covering the range from 70° N to 70° S (70° N/S) with a resolution of about 200 m/pixel were generated using the proposed RXP algorithm. Our results indicate that, compared with the result of a single data source, the use of IIM-CF data improved the accuracy of the modeling of oxide abundances and Mg#. It is expected that the CE-5 samples can bring additional references to the studies of the inversion for the oxides of the lunar surface and deepen our understanding over this issue.

Quantitative Inversion of Lunar Surface Chemistry Based on Hyperspectral Feature Bands and Extremely Randomized Trees Algorithm

In situ resource utilization (ISRU) is required for the operation of both medium and long-term exploration missions to provide metallic materials for the construction of lunar base infrastructure and H2O and O2 for life support. The study of the distribution of the lunar surface elements (Fe, Ti, Al, and Si) is the basis for the in situ utilization of mineral resources. With the arrival of the era of big data, the application of big data concepts and technical methods to lunar surface chemistry inversion has become an inevitable trend. This paper is guided by big data theory, and the Apollo 17 region and the area near the Copernicus crater are selected for analysis. The dimensionality of the first-order differential spectral features of lunar soil samples is reduced based on Pearson correlation analysis and the successive projections algorithm (SPA), and the extremely randomized trees (Extra-Trees) algorithm is applied to Chang’E-1 Interference Imaging Spectrometer (IIM) data to establish a prediction model for the lunar surface chemistry and generate FeO, TiO2, Al2O3, and SiO2 distribution maps. The results show that the optimum number of variables for FeO, TiO2, Al2O3, and SiO2 is 17, 5, 8, and 30, respectively. The accuracy of the Extra-Trees model using the best variables was improved over that of the original band model, with determination coefficients (R2) of 0.962, 0.944, 0.964, and 0.860 for FeO, TiO2, Al2O3, and SiO2, and root mean square errors (RMSEs) of 1.028, 0.672, 0.942, and 0.897, respectively. The modeling feature variables and model preference methods in this study can improve the inversion accuracy of chemical abundance to some extent, demonstrating the potential of IIM data in predicting chemical abundance and providing a good data basis for lunar geological evolution studies and ISRU.

A Fast and Effective Irregular Stripe Removal Method for Moon Mineralogy Mapper (M3)

Hyperspectral imagery (HSI) is one of the emerging tools to explore the physical properties and chemical composition of the lunar surface. Moon mineralogy mapper (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) is the most widely used lunar HSI data set with the widest coverage and the excellent resolution; however, dense and nonperiodic stripes distributed across all bands in M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> images hinder visual interpretation as well as their use in subsequent applications. In this article, a fast destriping approach for M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> is proposed using the Hodrick–Prescott decomposition embedded in the low-rank framework (LRHP) to overcome this limitation. The integration of a statistical filter and variational model tackles the problem stemming from a lack of the correct residual information when certain pixels are corrupted in every band, thereby restoring severely degraded hyperspectral images (HSIs). Simulated and real experiments conducted on typical regions on the Moon with various levels of corruption demonstrate that the proposed LRHP rapidly achieves favorable performance against state-of-the-art approaches. Also, expanding tests on interference imaging spectrometer (IIM) data of Chang’E-1 and commonly used terrestrial remote sensing images show that LRHP has good generalization capability. Moreover, the integrated band depth (IBD) maps further verify the necessity of destriping and the high spectral fidelity of LRHP that benefits further applications.

Adaptive Fringe Template of Temporally and Spatially Modulated Spatial Heterodyne Interference Imaging Spectrometer

Adaptive Fringe Template of Temporally and Spatially Modulated Spatial Heterodyne Interference Imaging Spectrometer

Characteristics of Step Surface Shape Error in Snapshot Interference Imaging Spectrometer

Characteristics of Step Surface Shape Error in Snapshot Interference Imaging Spectrometer

Motion Error Evaluation and Correction of Temporally and Spatially Modulated Spatial Heterodyne Interference Imaging Spectrometer

Motion Error Evaluation and Correction of Temporally and Spatially Modulated Spatial Heterodyne Interference Imaging Spectrometer

Correction of invalid data based on spatial dimension information of a temporally and spatially modulated spatial heterodyne interference imaging spectrometer.

Considering the distribution characteristics of interference data of a temporally and spatially modulated spatial heterodyne interference imaging spectrometer, an algorithm based on spatial dimension baseline of interference data for the detection and correction of invalid data is proposed. The intensity ratio of the target interference data far away from the zero optical path difference has been extracted and calculated, and the intensity of the interference data is compensated; the baseline of the compensated interference data is carried out along the spatial dimension direction, and the deviation matrix is calculated, and combined with the 3σ method for the detection and correction of invalid data. A simulation experiment is carried out in the laboratory to obtain the target push-sweep imaging interference data, and the spectrum is the output spectrum of the integrating sphere halogen tungsten lamp. The experimental results show that the invalid data in the interference data (including invalid data near zero optical path difference) can be effectively identified and corrected using the invalid data detection and correction algorithm described in this paper, which has a good effect on the correction of fixed invalid data and flash pixel.

Photometric Correction of Chang’E-1 Interference Imaging Spectrometer’s (IIM) Limited Observing Geometries Data with Hapke Model

The main objective of this study is to develop a Hapke photometric model that is suited for Chang’E-1 (CE-1) Interference Imaging Spectrometer (IIM) data. We first divided the moon into three areas including ‘maria’, ‘new highland’ and old ‘highland’ with similar photometry characteristic based on the Hapke parameters of the moon derived from Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) multispectral data. Then, we selected the sample data in the ‘maria’ area and obtained a new set of Hapke model’s parameters that can best fit these data. Result shows that photometric correction using Hapke model with these new derived parameters can eliminate the effect of variations in viewing and luminating geometry, especially ‘opposition surge’, more efficiently than the empirical model. The corrected mosaic shows no significant artifacts along the tile boundaries and more detailed information of the image can be exhibited due to a better correction of ‘opposition surge’ at small phase angle (g &lt; 15°).

Research on the optical axis of the birefringent crystal rotating in the three dimensional space

The beam splitting principle of the Gran-taylor prism as a birefringent crystal is explained. Using the ray tracing method, the angle of refraction of the extraordinary wave together with the direction of the extraordinary ray and its emitting position as a function of the incident angle θ1 and the angle θp between the optical axis and the normal are obtained in three-dimensional space. In order to analyze and discuss the influences of different parameters on the angle of refraction, the direction of the extraordinary ray and its emitting position, computers simulations are performed. If the deviation of θp is set as 5°, the biased error of the emitting position is 0.4274⁡mm in the y axis. In order to ensure that the deviation error for the emitting position is within 0.500⁡mm in the x axis, the incident angle should be controlled in a range of [0∘,1.702∘]. This study provides a theoretical and practical guidance for the industrial production of the polarization devices and the research of the polarization interference imaging spectrometer.

New maps of lunar surface chemistry

The major oxides (SiO2, Al2O3, CaO, FeO, MgO, and TiO2) and Mg# are critical for revealing the petrological characteristics of the Moon and for testing models of lunar formation and geologic evolution. There are few high-spatial-resolution (<250 m/pixel) abundance maps for all the six major oxides and Mg# across the Moon. Furthermore, previous studies primarily employed the traditional regression methods to derive oxide contents from optical images, which may influence the inversion accuracies of the lunar chemical compositions. This paper reports the abundance maps of all the six major oxides and Mg# with a relatively high spatial resolution of ∼200 m/pixel and compared them with the ones in the previous works. Neural networks algorithms along with the data from the Interference Imaging Spectrometer (IIM) onboard Chang'E-1 were employed in this paper to derive the abundances of the six oxides. Compared with the traditional linear regression models, the neural networks method suggested in this work is hopeful to better depict the complex nonlinear relations between the spectra and the chemical components, so it may improve the inversion performance of the lunar chemistry.

Automatic endmember bundle unmixing methodology for lunar regional area mineral mapping

The mineral distribution on lunar surface can contribute to studying lunar evolution, while abundance quantification is still challenging. Unmixing on spectral reflectance data is an effective way for mineral resource explanation, especially in hardly accessible area. In regional area unmixing, some existing unmixing models mainly rely on spectral libraries, which limits the scene adapability in the absence of some prior information. Meanwhile, spectral variation is a common phenomenon but often neglected, which may lead to subsequent abundance inversion errors. In this paper, we address a novel automatic image-based endmember bundle unmixing model, which is called AEBU, to solve these problems. Differently from many unmixing algorithms using a single spectrum to represent a type of mineral, we accommodate spectral variation and construct a set of spectra, i.e., endmember bundle, to represent each material, which will allow for comprehensive endmember expression. The endmember bundles are extracted from the imagery and regarded as a spectra catalog for abundance inversion to avoid the dependence on spectral library. The proposed AEBU model contains two major steps: image-based endmember bundle construction and abundance inversion. To construct endmember bundles effectively, we use pixel-wise sparse representation to extract image pixels as endmember candidates, and then analyze the shape feature of candidate spectra to separate endmember bundles. In abundance inversion, we consider the extracted endmember bundles as existing spectra library and propose a block sparse representation-based algorithm to automatically select reasonable endmembers for per-pixel unmixing. The performance of AEBU is compared with the state-of-the-art bundle unmixing algorithms on simulated lunar data. The experimental results demonstrate excellent performance of the proposed AEBU. Finally, we map the mineral distribution on lunar regional areas by AEBU using interference imaging spectrometer (IIM) data collected by ChangE-1 and moon mineralogy mapper (M3) data collected by Chandrayaan-1, and unmix the Cuprite data to show more application of AEBU.

The Absolute Reflectance and New Calibration Site of the Moon

Abstract How bright the Moon is forms a simple but fundamental and important question. Although numerous efforts have been made to answer this question such as use of sophisticated electro-optical measurements and suggestions for calibration sites, the answer is still debated. An in situ measurement with a calibration panel on the surface of the Moon is crucial for obtaining the accurate absolute reflectance and resolving the debate. China’s Chang’E-3 (CE-3) “Yutu” rover accomplished this type of measurement using the Visible-Near Infrared Spectrometer (VNIS). The measurements of the VNIS, which were at large emission and phase angles, complement existing measurements for the range of photometric geometry. The in situ reflectance shows that the CE-3 landing site is very dark with an average reflectance of 3.86% in the visible bands. The results are compared with recent mission instruments: the Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC), the Spectral Profiler (SP) on board the SELENE, the Moon Mineralogy Mapper (M3) on board the Chandrayaan-1, and the Chang’E-1 Interference Imaging Spectrometer (IIM). The differences in the measurements of these instruments are very large and indicate inherent differences in their absolute calibration. The M3 and IIM measurements are smaller than LROC WAC and SP, and the VNIS measurement falls between these two pairs. When using the Moon as a radiance source for the on-orbit calibration of spacecraft instruments, one should be cautious about the data. We propose that the CE-3 landing site, a young and homogeneous surface, should serve as the new calibration site.

Full linearly Stokes channeled polarimetric technique with low reconstruction errors

A novel full linearly Stokes channeled polarimetric technique is presented. The system includes an achromatic quarter wave plate, a high order retarder and interference imaging spectrometer. The principle of the system is verified by simulation. Compare with the conventional channeled polarimetric technique, the resolution of the reconstructed spectrum is remarkably improved and the errors in reconstructed spectral Stokes parameters caused by crosstalk are suppressed effectively. A compensation procedure is proposed to account for the alignment errors. An analytical treatment is given, followed by a numerical example to demonstrate the effectiveness of the compensation method.

Defringing in interference imaging spectrometer based on BEMD and PCA

The constructive and destructive fringe due to etaloning effects is an universal phenomenon emerging in the imaging system using the back-illuminated CCD. An adaptive method based on the bi-dimensional empirical mode decomposition (BEMD) and principal component analysis (PCA) was proposed to suppress the nonlinear fringe in interference imaging spectrometer. The feasibility was verified by reconstructing the fringe and interferogram taken by interference imaging spectrometer effectively. Meanwhile, the vertical CCD mosaic stripes was suppressed obviously. Comparing the retrieved contaminated and corrected spectrums, it was found that the sidelobes introduced by the nonlinear background was removed. It provides us a time-saving, without prior knowledge, and automatic approach for defringing.

Analysis of the Sagnac interference imaging spectrometer with a variable optical path difference

The Sagnac interference imaging spectrometer with a variable optical path difference (OPD) is proposed in this paper, which employs two wedge prisms coupled with a modified Sagnac interferometer, and produces a variable OPD through the moving wedge prism. Compared with the conventional imaging spectrometer, the Sagnac interference imaging spectrometer shows its advantages of miniaturization and insensitive to the non-uniform variation of the moving speed and the environment vibration. The exact expression of the OPD as a function of different parameters is derived, and the influences of the moving displacement, wedge angle and acute angles on the OPD are analyzed and discussed within the scope of engineering design. This study provides an important theoretical and practical guidance for the engineering of the Sagnac interference imaging spectrometer.

Bi-dimensional empirical mode decomposition based fringe-like pattern suppression in polarization interference imaging spectrometer

Many observers using interference imaging spectrometer were plagued by the fringe-like pattern(FP) that occurs for optical wavelengths in red and near-infrared region. It brings us more difficulties in the data processing such as the spectrum calibration, information retrieval, and so on. An adaptive method based on the bi-dimensional empirical mode decomposition was developed to suppress the nonlinear FP in polarization interference imaging spectrometer. The FP and corrected interferogram were separated effectively. Meanwhile, the stripes introduced by CCD mosaic was suppressed. The nonlinear interferogram background removal and the spectrum distortion correction were implemented as well. It provides us an alternative method to adaptively suppress the nonlinear FP without prior experimental data and knowledge. This approach potentially is a powerful tool in the fields of Fourier transform spectroscopy, holographic imaging, optical measurement based on moire fringe, etc.

New Insights Into Lithology Distribution Across the Moon

AbstractLithology distribution across the Moon is pivotal for understanding lunar evolution. However, so far, the distribution of lunar rock suites is still uncertain; as a result, many related core issues on lunar evolution have long been in dispute. This work reports on a new lithology distribution map across the Moon and discusses some critical issues of the lunar evolutionary process. The oxide abundances derived from Chang'E‐1 Interference Imaging Spectrometer imagery and the Th contents inferred by Lunar Prospector Gamma Ray and Neutron Spectrometer data are employed to generate the lithological map by using the decision tree C5.0 algorithm. The following conclusions are inferred from this new map. (1) Magnesian suite is widely distributed across the Feldspathic Highlands Terrane and in the periphery of the South Pole‐Aitken Terrane. Thus, the viewpoints have been validated that the early magnesian magmatism may be a global phenomenon and that KREEP basalt is not necessary for the petrogenesis of Mg‐rich rocks. Moreover, the regions of Dryden, Chaffee S, Theophilus, and Moscoviense are confirmed as magnesian suite exposures. (2) The observation that the Feldspathic Highlands Terrane has a higher Mg/(Mg + Fe) value than the maria is related to the flood of the Mg suite across the Feldspathic Highlands Terrane. (3) The specific exposed locations of the alkali suite across the Moon have long been unsolved, and this work discloses that the alkali suite prevails in the outskirts of the Procellarum KREEP Terrane, the center of the South Pole‐Aitken Terrane, and some isolated locales. (4) Focusing on distinguishing mare basalts from other mafic rocks, seven geochemical indices are proposed to determine the potential exposures of mare basalts across the Moon. (5) In Mare Insularum, a series of KREEP volcanisms may have occurred and lasted longer than the mare volcanism.

Wavelet transform based defringing in interference imaging spectrometer.

The constructive and destructive fringe-like pattern (FP) introduced by the fringing effects is a universal phenomenon emerging in the imaging system using the back-illuminated CCD. Generally, the flat fielding or modeling based methods were applied to suppressing the FP and featured as time-consuming, duplicated, and hardware-based. In this paper, a method based on the wavelet transform was proposed for the interferogram processing in interference imaging spectrometer. An artificial interferogram construction method was developed and utilized to evaluate the quality of the reconstructed interferogram. The performance of defringing was significantly determined by the wavelet decomposition. Through numerical simulation, 4 wavelets were selected out of 50 typical wavelets; the decomposition levels with better performance were determined. The feasibility of the defringing and performance evaluation methods were verified by the simulation and practical experiments. It provides us with a software-based, time-saving, without prior knowledge, automatic approach for defringing.

Linear stokes imaging spectropolarimeter based on the static polarization interference imaging spectrometer

The theoretical operation and experimental demonstration of a Fourier-transform linear imaging spectropolarimeter are presented. It is composed of a rotating Glan-Taylor prism and a Fourier-transform spectrometer based on Savart polariscope. The polarized light enters the spectrometer to create three sets of interferograms, where the spectral linear Stokes parameters can be calculated and acquired. Compared with previous instruments, the significant advantages of the described sensor are that there are no spatial aliasing in the polarized spectra and it can be used in wider spectral coverage with low cost, ultra-compact size and a simpler common-path configuration. Another static linearly Stokes imaging spectropolarimeter based on the field of view division technique and SPIIS is conceptually described. The spectral dependence of linear Stokes parameters can be recovered with Fourier transformation. Since there is no rotating or moving parts, the system is relatively robust.

Heterodyne polarization interference imaging spectroscopy

A novel heterodyne polarization interference imaging spectroscopy (HPⅡS) based on a Savart polariscope is proposed in this paper. The HPⅡS is modified by introducing a pair of parallel polarization gratings into the static polarization interference imaging spectrometer. Because of the introduced parallel polarization gratings, the lateral displacements of the two beams split by the Savart polariscope vary with wavenumber. The frequency of the interferogram obtained on the detector is related to wavenumber. Like the spatial heterodyne spectrometer where the two end mirrors in a Michelson interferometer are replaced with two matched diffraction gratings, the zero frequency of the interferogram generated in HPⅡS corresponds to a heterodyne wavenumber instead of the zero wavenumber in a non-heterodyne spectrometer. Due to the heterodyne characteristics, a high spectral resolution can be achieved using a small number of sampling points. In addition, there is no slit in HPⅡS and it is an imaging Fourier transform spectrometer that records a two-dimensional image of a scene superimposed with interference curves. It is a temporally and spatially combined modulated Fourier transform spectrometer and the interferogram of one point from the scene is generated by picking up the corresponding pixels from a sequence of images which are acquired by scanning the scene. As a true imaging spectrometer, HPⅡS also has high sensitivity and high signal-to-noise ratio. In this paper, the basic principle of HPⅡS is studied. The optical path difference produced by the Savart polariscope and the parallel polarization gratings is calculated. The interferogram expression, the spectral resolution, and the spectrum reconstruction method are elaborated. As the relationship between the frequency of the interferogram and the wavenumber of the incident light is nonlinear, the input spectrum can be recovered using Fourier transform combined with the method of stationary phase. Also, the matrix inversion method can be used to recover the input spectrum. Finally, a design example of HPⅡS is given. The interferogram is simulated, and the recovered spectrum shows good agreement with the input spectrum. In the design example, the spectral range is 16667-18182 cm-1(550-600 nm), and the number of sampling points is 500. The spectral resolution of HPⅡS is 6.06 cm-1, which is 12 times smaller than that in a non-heterodyne spectrometer with the same spectral range and sampling numbers. HPⅡS has the advantages of compact structure, high optical throughput, strong stability, and high spectral resolution. It is especially suitable for hyperspectral detection with ultra-small, high stability, and high sensitivity.