Push-broom Mode Research Articles

High-Resolution Nitrogen Dioxide Measurements from an Airborne Fiber Imaging Spectrometer over Tangshan, China

The pollution caused by nitrogen dioxide is a major environmental problem in China. This study introduces a new type of atmospheric trace gas remote-sensing instrument, an airborne fiber imaging spectrometer. This spectrometer has a spectral range of 300–410 nm and works in push-broom mode with a 30° field of view on a flight path. Flight experiments were conducted on 30 December 2022 and 5 January 2023, covering heavily polluted areas east of Beijing and Tangshan. This equipment obtained the density distribution of NO2 over the flight area. The results showed that pollution was mainly concentrated in the Caofeidian area and at the power station in the north, and the main source of pollution was anthropogenic. Satellite and airborne data near the pollution points were compared, and the two datasets showed a positive correlation with a correlation coefficient of 0.78 and 0.7, on the two days, respectively. This study demonstrates the capability of an airborne fiber imaging spectrometer for NO2 regional emission remote sensing and identifying the pollution points.

Single-Image Simultaneous Destriping and Denoising: Double Low-Rank Property

When a remote sensing camera work in push-broom mode, the obtained image usually contains significant stripe noise and random noise due to differences in detector response and environmental factors. Traditional approaches typically treat them as two independent problems and process the image sequentially, which not only increases the risk of information loss and structural damage, but also faces the situation of noise mutual influence. To overcome the drawbacks of traditional methods, this paper leverages the double low-rank characteristics in the underlying prior of degraded images and presents a novel approach for addressing both destriping and denoising tasks simultaneously. We utilize the commonality that both can be treated as inverse problems and place them in the same optimization framework, while designing an alternating direction method of multipliers (ADMM) strategy for solving them, achieving the synchronous removal of both stripe noise and random noise. Compared with traditional approaches, synchronous denoising technology can more accurately evaluate the distribution characteristics of noise, better utilize the original information of the image, and achieve better destriping and denoising results. To assess the efficacy of the proposed algorithm, extensive simulations and experiments were conducted in this paper. The results show that compared with state-of-the-art algorithms, the proposed method can more effectively suppress random noise, achieve better synchronous denoising results, and it exhibits a stronger robustness.

The Design of Cone and Pendulum Scanning Mode Using Dual-Camera with Multi-Dimensional Motion Imaging Micro-Nanosatellite

This paper focuses on the design of a new optical cone and pendulum scanning imaging mode for micro-nanosatellites. This kind of satellite uses a high-resolution camera with a small imaging plane to achieve high-resolution and ultra-wide coverage imaging through the three-dimensional motion of the camera’s wobble, satellite spin, and satellite orbital motion. First, this paper designs a single-camera constant speed OCPSI (optical cone and pendulum scanning imaging) mode. On the premise of ensuring coverage, the motion parameters and imaging parameters are derived. Then, in order to improve the performance and imaging quality of the system, a dual-camera variable speed OCPSI mode is designed. In this method, in order to reduce the overlap ratio, the camera is oscillated at a variable speed. Turn on the cameras in turn at the same time to minimize the overlap. This paper details these working modes. The simulation experiment is carried out using the satellite orbit of 500 km, the focal length of 360 mm, the pixel size of 2.5 μm, the resolution of [5120 × 5120], the number of imaging frames in the pendulum scanning hoop of 10, and the initial camera inclination angle of 30°. The single-camera constant speed OCPSI mode has an effective swath of 1060 km at a ground sampling distance of 5.3 m. The dual-camera variable speed OCPSI mode has an effective width of 966 km under the same conditions. Finally, the ground experiment prototype of OCPSI imaging theory is designed. We choose a camera with a pixel size of 3.45 μm, a resolution of [1440 × 1080], and a focal length of 25 mm. The ground experiment was carried out at the initial camera inclination angle of 10°, the number of imaging frames in the pendulum scanning hoop of 3, and the orbit height of 11 m. The experimental result is that the effective width of OCPSI imaging mode reaches 10.8 m. Compared with the traditional push-broom mode using the same camera, the effective width of 1.64 m is increased by seven times, and the effective width of 3.83 m is increased by three times compared to the traditional whisk-broom imaging mode. This study innovatively integrates three-dimensional motion imaging into aerospace remote sensing and provides a reference for the research on the realization of high-resolution and ultra-wide coverage of micro-nano remote sensing satellites.

Jitter Detection and Image Restoration Based on Continue Dynamic Shooting Model for High-Resolution TDI CCD Satellite Images

Although time delay integration charge-coupled devices (TDI CCDs) have been widely used in high-resolution spaceborne optical cameras, they are sensitive to satellite jitter: the images obtained by them are affected by both distortion and blur. Therefore, according to the multistage integral imaging characteristics of TDI CCDs, this article not only proposes a continue dynamic shooting model (CDSM) to reflect the real push-broom mode of the satellite but also presents a method containing jitter detection and image restoration based on it. In the presented method, the CDSM subdivides the TDI CCD integration intervals. The subdivision number of CDSM is determined by the proposed integral transformation function (ITF). Then, it feeds back into the ITF and also contributes to the point spread function (PSF) estimation. Among the abovementioned, ITF defines the relationship between the parallax images and the jitter curve, and aims to improve the jitter detection performance. Finally, an adaptive image restoration based on context is conducted, which combines time, space, and spectrum information. Besides the simulated images, multispectral images of GaoFen-1 02 satellite were also adopted to validate the performance of the presented method. Experimental results indicate that the accuracy of the jitter detection is increased, and the geometric and radiometric qualities of restored images are also improved.

Hadamard transform-based hyperspectral imaging using a single-pixel detector.

In this paper, a single-pixel hyperspectral imager is developed based on the Hadamard transformation. The imager's design, fabrication, signal processing method, and experimental results are discussed. The single-pixel hyperspectral imager works in pushbroom mode and employs both spatial encoding and spectral encoding to acquire the hyperspectral data cube. Hadamard encoding patterns, which are known for their multiplexing advantage to achieve high signal-to-noise ratio (SNR), are used in both encoding schemes. A digital micromirror device (DMD) from Texas Instruments (TI) is used for slow spatial encoding and a resonant scanning mirror in combination with a fixed Hadamard mask is used for fast spectral encoding. In addition, the pushbroom operation can be achieved internally by spatially shifting the location of the Hadamard encoded slit on the DMD, thus the imager is able to acquire 3D data cubes without the need to scan it across the object. Although our experimental results demonstrate the hyperspectral data cubes of various objects over a 450 nm ∼ 750 nm visible spectral range, the proposed imager can be easily configured to be used at other wavelengths due to the single-pixel detection mechanism used.

Numerical Focusing of a Wide-Field-Angle Earth Radiation Budget Imager Using an Artificial Neural Network

Narrow field-of-view scanning thermistor bolometer radiometers have traditionally been used to monitor the earth’s radiant energy budget from low earth orbit (LEO). Such instruments use a combination of cross-path scanning and along-path spacecraft motion to obtain a patchwork of punctual observations which are ultimately assembled into a mosaic. Monitoring has also been achieved using non-scanning instruments operating in a push-broom mode in LOE and imagers operating in geostationary orbit. The current contribution considers a fourth possibility, that of an imager operating in LEO. The system under consideration consists of a Ritchey-Chrétien telescope illuminating a plane two-dimensional microbolometer array. At large field angles, the focal length of the candidate instrument is field-angle dependent, resulting in a blurred image in the readout plane. Presented is a full-field focusing algorithm based on an artificial neural network (ANN). Absorbed power distributions on the microbolometer array produced by discretized scenes are obtained using a high-fidelity Monte Carlo ray-trace (MCRT) model of the imager. The resulting readout array/scene pairs are then used to train an ANN. We demonstrate that a properly trained ANN can be used to convert the readout power distribution into an accurate image of the corresponding discretized scene. This opens the possibility of using an ANN based on a high-fidelity imager model for numerical focusing of an actual imager.

Performance of Dual-Band Short-Wave Infrared InGaAs Focal-Plane Arrays with Interference Narrow-Band Filter

In this work, we fabricated dual-band 800 × 2 short-wave infrared (SWIR) indium gallium arsenide (InGaAs) focal-plane arrays (FPAs) using N-InP/i-In0.53Ga0.47As/N-InP double-heterostructure materials, which are often applied in ocean-color remote sensing. Using narrow-band interference-filter integration, our detector-adopted planner structure produced two detection channels with center wavelengths of 1.24 and 1.64 μm, and a full-width half-maximum (FWHM) of 0.02 μm for both channels. The photoelectric characteristics of the spectral response, modulation transfer function (MTF), and detectability of the detector were further analyzed. Our FPAs showed good MTF uniformity with pixel operability as high as 100% for each 800 × 1 linear array. Peak detectivity reached 4.39 × 1012 and 5.82 × 1012 cm·Hz1/2/W at 278 K, respectively, and response nonuniformity was ideal at 2.48% and 2.61%, respectively. As a final step, dual-band infrared detection imaging was successfully carried out in push-broom mode.

Modified Sagnac imaging spectropolarimeter for full linear Stokes parameters

A modified Sagnac imaging spectropolarimeter is conceptually described. It consists of a spectral-polarimetric modulator, a modified Sagnac interferometer with large optical path difference, and a CCD camera. This design modulates the Stokes components of the input light into different wave numbers and obtains the modulated interferogram in snapshot mode, and the spectra of the Stokes components can be separated and demodulated from the interferogram. The performance of the system is demonstrated through a numerical simulation, and a novel method is proposed to detect the polarization parameters including the degree of polarization and polarization direction for eliminating the aliasing effects between linear Stokes parameters. Compared with the existing imaging spectrometers, the modified Sagnac imaging spectropolarimeter can acquire one-dimensional spatial information and its full linear spectropolarimetric information in one exposure, and some other spatial information can be obtained by push-broom mode.

Subpixel three-dimensional laser imaging with a downscaled avalanche photodiode array using code division multiple access

Scannerless time-of-flight three-dimensional imaging, the successor to raster scanning three-dimensional imaging, relies on large-scale detector arrays to obtain high pixel resolution; however, manufacturing limitations lead to a bottleneck in imaging resolution. Here, we report a methodology for laser imaging using code division multiple access, which involves three key steps. Optical encoding is carried out for a pulsed laser to generate space-time encoded beams for projection. Optical multiplexing subdivides the backscattered light signals and multiplexes them to a downscaled avalanche-photodiode array. Subpixel decoding decodes the digitized encoded full waveforms and decomposes the features of all subpixels. Accordingly, we design a prototype based on a 64-order encoder and a 4-element avalanche-photodiode array and conduct an outdoor experiment. We demonstrate that the system is capable of obtaining 256 pixels per frame in push-broom mode and reconstruct a three-dimensional image with centimetre-level lateral resolution and range precision at a distance of ∼112 m.

Development of method for active alignment of multiple time delay and integration detectors in the optically butted focal plane assembly of high-resolution spaceborne imaging systems

Time delay and integration (TDI) detectors are preferred image sensors for high-resolution spaceborne imaging systems for cartographic applications as they provide higher sensitivity by integrating charges over multiple TDI stages in push broom mode. Large swath requirements are met using multiple TDI detectors in optical butting configuration in the focal plane assembly (FPA) to form a single image line on the ground. These detectors need to be aligned with subpixel accuracy to avoid motion smear and errors in the image mosaicking process. Alignment of the multiple TDI detectors in the FPA is a challenging task and is accomplished using custom methods and setups. Passive alignment techniques rely on very high-resolution microscopes for achieving desired accuracies. Active method requires TDI detectors to be operated in staring mode, which is architecturally and functionally not supported by TDI detectors. We developed a scheme for operating the TDI detectors in staring mode without any smear effects to aid in the active alignment process. Based on this, we propose an active alignment approach. The proposed approach is highly advantageous as it can be used throughout the imaging system development phase to demonstrate stability of the alignment and also helps in cross validation with the passive alignment. The developed method was test validated on qualification model FPA, and alignment accuracy of the order of 0.4 μm in tilt and 1.2 μm in line shift has been demonstrated, against the requirements of ±1.5 μm. This method has been extensively used in Cartosat-2S series imaging systems and will be very useful for upcoming high-resolution missions of the Indian Space Research Organisation.

Modeling and image motion analysis of parallel complementary compressive sensing imaging system

Based on the theory of compressive sensing, a parallel complementary compressive sensing imaging system is proposed, and the mathematical model of block parallel processing is established. Parametric analysis shows that the quality of the restored image increases with the increase of observed compression ratio and the decrease of the number of blocks, which is in conflict with total amount of data and time-consuming of algorithm, and needs to be considered comprehensively. According to the demand of space remote sensing system applied in push-broom mode, the image motion model of the system is established. The results show that the image motion has a severe effect on the quality of restored image, and increasingly responsive with the decrease of the number of blocks. when the orbital image motion parameter is constant, improving the frame rate of the detector and increasing the pixel size can obtain a smaller image motion ratio, thereby enhancing the image quality. But the application scope of the system for push-broom imaging is somewhat limited for its significantly degrade under low image motion ratio.

Ground-based Observation System Development for the Moon Hyper-spectral Imaging

The Moon provides a suitable radiance source for on-orbit calibration of space-borne optical instruments. A ground-based observation system dedicated to the hyper-spectral radiometry of the Moon has been developed for improving and validating the current lunar model. The observation instrument using a dispersive imaging spectrometer is particularly designed for high-accuracy observations of the lunar radiance. The simulation and analysis of the push-broom mechanism is made in detail for lunar observations, and the automated tracking and scanning is well accomplished in different observational condition. A three-month series of hyper-spectral imaging experiments of the Moon have been performed in the wavelength range from 400 to 1000 nm near Lijiang Observatory (Yunnan, China) at phase angles −83°–87°. Preliminary results and data comparison are presented, and it shows the instrument performance and lunar observation capability of this system are well validated. Beyond previous measurements, this observation system provides the entire lunar disk images of continuous spectral coverage by adopting the push-broom mode with special scanning scheme and leads to the further research of lunar photometric model.

Analysis on the simplified optic coma effect on spectral image inversion of coded aperture spectral imager

With the novel spectrum imaging technology development in recent years, the push-broom coded-aperture spectral imaging (PCASI) shows the advantages of high throughput, high SNR, high stability etc. This coded-aperture spectral imaging utilizes fixed-code templates and push-broom mode, which can realize high-precision reconstruction of spatial and spectral information. But during optical lens designing, manufacturing and debugging, there inevitably exist some minor coma errors. Even minor coma errors can reduce image quality. In this paper, we simulate the system optical coma error which influences the quality of reconstructed image, analyze the variantion of the coded aperture in different optical coma effect, and then propose an accurate curve for image quality and optic coma quality in 255× 255 coded template, which provides important references for the design and development of push-broom coded-aperture spectrometer.

On optimization of attitude control programs for earth remote sensing satellite

The paper considers the problem of attitude control of Earth remote sensing satellite (RSS) while scanning geometrically complex paths (in push broom mode) with preliminary redirecting optoelectronic sensing equipment. The model of a control pattern is given, which is an elementary operation in development of integral control programs on multiturn flight intervals. The pattern consists of two sequential RSS control maneuvers: redirecting and scanning. The problem of optimizing the control pattern is formulated. The problem of RSS optimal attitude control for redirecting maneuver, as a part of optimization problem, is solved. The solution method suitable for integration of control programs is presented.

Absolute misalignment estimation with respect to a scanning image sensor

This letter proposes a simple but effective method for in-flight estimation of absolute misalignment, which is defined as the orientation offset error between attitude sensors and an imaging payload. The method was developed for high-resolution spaceborne/airborne imaging systems, which use a scanning image sensor in their payload. This type of image sensor operates in the pushbroom mode, so that previously existing methods are not easily applicable. The proposed method utilizes the pre-existing attitude-determination algorithms originally used to estimate the attitude of a star tracker equipped with a planar image sensor. We converted the geo-referencing relation between the GCP (Ground Control Point) directions and their image vectors into a new expression which enables the application of the attitude-determination algorithms to identify the absolute misalignment. Pointing knowledge analysis, using actual in-flight data, is presented to verify the developed method.

Experimental measurement of aluminium diffuser applied to calibration system of space-borne differential optical absorption spectrometer

In a space-borne differential optical absorption spectrometer, which has a large field in nadir push-broom mode the “Sun+Diffuser” method is adopted for onboard spectral calibration. Therefore the aluminium diffuser used in the space-borne spectral calibration system is required to have a good Lambert feature to ensure the full field spectral calibration accuracy of the space-borne differential optical absorption spectrometer. And it can provide a uniform source in the observing view-field of the instrument. Using bidirectional reflectance distribution function measurement instrument, bidirectional reflectance distribution function of aluminium diffuser is measured by the relative measurement method. Experimental results show that in a wavelength range of 180–880 nm and an observing view range from -70° to +70°, the bidirectional reflectance distribution function declines from middle to both sides and approximates the cosine distribution, showing that the aluminium diffuser has a good Lambert feature. The spectral calibration of the space-borne instrument is also presented with the system: high calibration accuracy is reached by the calibration system, with the maximum deviation being 0.022 nm, which meets the requirements for the accuracy better than 0.05 nm. The aluminium diffuser measured in laboratory can be chosen for the spectral calibration system.

Broadband QWIP FPAs for hyperspectral applications

Is a quantum well infrared photodetector (QWIP) suitable for hyperspectral applications? Yes, provided its spectral response is broad enough, the signal-to-noise ratio in narrow spectral slices across the entire response band is high enough, and the operating temperature is reasonable. We present the performance of a 640×512 QWIP focal plane array (FPA) with nearly uniform spectral response from 8 to 12μm that achieves temporal noise equivalent temperature difference (NETD) lower than 200mK in 20nm wide spectral slices across the entire 8–12μm band with the FPA operating at a temperature of 50K or colder. A hyperspectral camera would feature a grating or prism to disperse 8–12μm light across such a FPA or a hyperspectral filter on top of the FPA. Operating in pushbroom mode on an earth-observing satellite, the camera can be used for spectral mapping of vegetation, crops and forests, for pollution monitoring, and for studies in atmospheric chemistry.

QWIP-based thermal infrared sensor for the Landsat Data Continuity Mission

The thermal infrared sensor (TIRS) is a QWIP based instrument intended to supplement the Operational Land Imager (OLI) for the Landsat Data Continuity Mission (LDCM) [See Landsat project description at: http://landsathandbook.gsfc.nasa.gov/handbook/handbook_htmls/chapter1/chapter1.html, [1]. The LDCM is planned to be launched in late 2012 and will continue the 35 year legacy of the Landsat program as Landsat 7 degrades. The LDCM is a joint NASA–US Geological Survey (USGS) mission. The TIRS instrument is a far infrared imager operating in the push broom mode with two IR channels: 10.8 μm and 12 μm. The focal plane will contain three 640 × 512 QWIP arrays mounted on a silicon substrate. The readout integrated circuit (ROIC) is intended to be the Indigo 9803. The focal plane operating temperature will be 43 K (nominally). Bandpass filters will define the precise spectral response of the focal plane. Two QWIP designs will be pursued, the corrugated structure and the grating structure. NASA/Goddard, the Army Research Lab and QmagiQ will work closely together to obtain the suite of arrays that will best meet the mission requirements (primarily adequate conversion efficiency at the required wavelengths). This paper will describe the design and fabrication of the TIRS instrument with particular emphasis on the QWIP detectors. The QWIP parameters that are driving the mission requirements include spectral response, dark current, conversion efficiency, read noise, temperature stability, pixel uniformity and pixel yield. Additional mechanical constraints such as co-registration between the three arrays, filter design and assembly and testing will also be discussed.

Terrain mapping camera for Chandrayaan-1

The Terrain Mapping Camera (TMC) on India’s first satellite for lunar exploration, Chandrayaan-1, is for generating high-resolution 3-dimensional maps of the Moon. With this instrument, a complete topographic map of the Moon with 5 m spatial resolution and 10-bit quantization will be available for scientific studies. The TMC will image within the panchromatic spectral band of 0.4 to 0.9 Μm with a stereo view in the fore, nadir and aft directions of the spacecraft movement and have a B/H ratio of 1. The swath coverage will be 20 km. The camera is configured for imaging in the push broom-mode with three linear detectors in the image plane. The camera will have four gain settings to cover the varying illumination conditions of the Moon. Additionally, a provision of imaging with reduced resolution, for improving Signal-to-Noise Ratio (SNR) in polar regions, which have poor illumination conditions throughout, has been made. SNR of better than 100 is expected in the ±60° latitude region for mature mare soil, which is one of the darkest regions on the lunar surface. This paper presents a brief description of the TMC instrument.

Development and Calibration of the Airborne Three-Line Scanner (TLS) Imaging System

for a large number of ground control points (GCP) for georeferThe Airborne Three-Line-Scanner (TLS) imaging system has encing the imagery. These developments offer new possibilities provided proof of the concept of stereo and multispectral for the production such as digital surface/terrain models, mapping using the pushbroom mode because frame digital orthoimages, and classification maps (Fritsch and Stallmann, imaging systems with comparable coverage and resolution 2000). have not been available and are not likely to be available in On the other hand, progress in the development of airborne the future. A prototype of the TLS system, the STARIMAGER, was linear imaging systems has been made in the last decades. developed jointly in 2000 by the STARLABO Corporation of These sensors can provide higher resolution and repeated temJapan and the University of Tokyo and is introduced in this poral panchromatic, multispectral, and hyperspectral image paper. A laboratory method and algorithm to evaluate the data for mapping and GIS applications (Tempelmann et al., optical characteristics of STARIMAGER are presented. The 2000). The Digital Photogrammetry Assembly (DPA) was finprinciple is to measure the object-space angles of a sufficient ished and tested in 1995 by the Institute of Photogrammetry, number of CCD elements in two directions as seen through the University of Stuttgart to produce 1:25,000- and 1:50,000-scale optics. These angular measurements reflect the real camera maps, and to automatically generate a DTM to accuracies of betgeometry of both the optics and the CCD arrays. A mathe- ter than 3 m (Hahn et al., 1996). The ADS40 airborne digital matical model based on the central perspective projection has sensor, developed in 2000 by LH Systems, has been tested in