Target discrimination is of great significance in many applications such as remote sensing, security monitoring, production testing and so on. Nowadays accurate target discrimination is often resorted to spectral imaging technique due to its high-resolution spectral/spatial information acquisition ability as well as plenty of data processing methods. In this paper, hyper-spectral imaging technique together with spectral generalized angle analysis method is used to solve camouflage target discrimination problem. A self-developed visual-band hyper-spectral imaging device is adopted to collect data cubes of certain experimental scene before spectral generalized angle is worked out so as to discriminate abnormal target. Full-band spectral generalized angle is measured to evaluate target discrimination effect visually and quantitatively. This is proved to be an effective tool for target detection task and can be further developed for other imaging techniques beyond spectral imaging.
Anomaly detection is helpful in many applications such as food monitoring, production testing, security surveillance, military countermeasure and so on. Spectral imaging technique is often resorted to for accurate abnormal target discrimination due to its high-resolution spectral/spatial information acquisition ability and a great number of data processing methods. Anomaly detection methods for hyperspectral imagery are contrastively studied in this paper. A self-developed visual-band hyperspectral imaging spectrometer is adopted to collect data cubes of certain experimental scene before two kinds of spectral-domain descriptors are used to execute abnormal camouflage detection. Detection effect of information divergence and generalized angle that are utilized as detection descriptors is visually and quantitatively compared and time consumption is assessed. The study is proved to be of significance to meet the anomaly detection demand that is based on spectral signature comparison and can be developed for further detection descriptor study and other imaging techniques beyond spectral imaging.
Target detection is one of most important applications in remote sensing. Nowadays accurate camouflage target distinction is often resorted to spectral imaging technique due to its high-resolution spectral/spatial information acquisition ability as well as plenty of data processing methods. In this paper, hyper-spectral imaging technique together with spectral information divergence measure method is used to solve camouflage target detection problem. A self-developed visual-band hyper-spectral imaging device is adopted to collect data cubes of certain experimental scene before spectral information divergences are worked out so as to discriminate target camouflage and anomaly. Full-band information divergences are measured to evaluate target detection effect visually and quantitatively. Information divergence measurement is proved to be a low-cost and effective tool for target detection task and can be further developed to other target detection applications beyond spectral imaging technique.
Proc. SPIE. 9685, 8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Micro- and Nano-Optical Devices and Systems; and Smart Structures and Materials
Optical design of a novel optical imaging system is presented. It can overcome the scaling of the aberrations by dividing the imaging task between a single objective lens that achieves a partially corrected intermediate image on a spherical surface, and an array of micro-lens, each of which relays a small portion of the intermediate image to its respective sensor, correcting the residual aberrations. The system is aimed for obtaining large field-of-view without deteriorating its resolution, of which traditionally designed optical imaging systems have met great difficult. This progress not only breaks through the traditional restrictions, but also allows a wider application for optical imaging systems. Firstly, proper configuration, which satisfies both the requirement of compactness and high performance, is determined according to the working principle of the novel system and through the research of the design idea in this paper. Then, a design example is presented with the field-of-view 50°and its resolution 0.2mrad, which remains as the field-of-view scales. But the optimized scalable system is of close packed structure and its dimension is less than 300mm along the ray incidence.
Recent research in the area of image quality assessment has been focusing almost exclusively on greyscale and color images. The advent of technologies such as remote sensing, biomedical and industrial imaging however demands this research to be extended to multi/hyper spectral images. Spectral imaging has more judging essentials than greyscale or color imaging and its image quality assessment task intends to cover up all-around evaluating factors. This paper presents an integrating spectral imaging quality assessment project, in which spectral-based, spatial-based and radiometric-based quality evaluation behavior for one remote-sensing hyperspectral imager are jointly executed. Spectral response function is worked out and spectral performance is further judged according to its FWHM and spectral excursion value. Spatial quality assessment is worked out by MTF computing with an improved slanted edge analysis method. Radiometric response ability of different spectral channels is judged by SNR computing based upon local RMS extraction and statistics method. Improved noise elimination and parameter optimization method are adopted to improve the evaluation fidelity. This work on spectral imaging quality assessment not only has significance in the development of on-ground and in-orbit spectral imaging technique but also takes on reference value for index demonstration and design optimization for spectral instrument development.
The imaging spectro-polarimetry combines the spectral imaging technology and the imaging polarization technology. It assembles the functions of camera, spectrometer and polarimeter. So the optical information quantity is increased and the detection efficiency is improved. But the acquirement of the multi-dimensional information results in the detector complex construction and large volume. The moving part is used in the current method to realize the different polarization states or spectral filtering. The images are difficult for registration and the current method can’t be used to get the motion scene. This paper presents innovative imaging spectro-polarimetry method with no moving parts. The hyper-spectral information, full-Stokes polarization information and one-dimensional spatial information are obtained by the polarization modulating and spectrum dispersing. The designed imaging spectro-polarimeter is composed of two parts, a polarization module and the spectral dispersive module. They are all employed stationary configuration. The polarization module includes two birefringent crystal wave plates and a polarizer. The thickness of the birefringent wave-plates and the polarization axes of each component are optimized and the full-Stokes polarization information is loaded on the spectrum. The polarization information can be restored by the Fourier transform. The concentric Offner configuration is adopted for spectral dispersive module. It is composed of two concave spherical mirrors and a holographic aberration-corrected convex grating. The designed dispersive configuration is compact and aligned simply. And high quality linear dispersion, low distortion spectral image are implemented. The Full-stokes imaging spectro-polarimeter our designed is validated by the model simulation and the laboratory experiment. The mixed hyper-spectral information and accuracy polarization information can be obtained.
A novel snapshot imaging spectrometer with large field-of-view (FOV) up to 100° is achieved by taking the advantages of a multiscale fore-optics and a compact Offner imaging spectrograph. Based on the diffraction imaging theory, the multiscale fore-optics composed of a monocentric spherical lens and multi-channel microlens array is designed, over which panchromatic images with small FOV are of uniform image quality. And identical imaging spectrographs with a dimension less than 30 cubic millimeters and with a high spectral resolution of about 2nm are designed correspondingly. The presented imaging spectrometer works at the visible wavelength range which is from 400nm to 780nm. It is of a fast speed about F/2.4 and a compact configuration of only 200mm×300mm×300mm in dimension. But the smile and keystone distortions are negligible.
Image quality assessment is an essential value judgement approach for many applications. Multi & hyper spectral
imaging has more judging essentials than grey scale or RGB imaging and its image quality assessment job has to cover
up all-around evaluating factors. This paper presents an integrating spectral imaging quality assessment project, in which
spectral-based, radiometric-based and spatial-based statistical behavior for three hyperspectral imagers are jointly
executed. Spectral response function is worked out based on discrete illumination images and its spectral performance is
deduced according to its FWHM and spectral excursion value. Radiometric response ability of different spectral channel
under both on-ground and airborne imaging condition is judged by SNR computing based upon local RMS extraction
and statistics method. Spatial response evaluation of the spectral imaging instrument is worked out by MTF computing
with slanted edge analysis method. Reported pioneering systemic work in hyperspectral imaging quality assessment is
carried out with the help of several domestic dominating work units, which not only has significance in the development
of on-ground and in-orbit instrument performance evaluation technique but also takes on reference value for index
demonstration and design optimization for instrument development.
The radiometric calibration of imaging spectrometer plays an import role for scientific application of spectral data. The radiometric calibration accuracy is influenced by many factors, such as the stability and uniformity of light source, the transfer precision of radiation standard and so on. But the deviation from the linear response mode and the polarization effect of the imaging spectrometer are always neglected. In this paper, the linear radiometric calibration model is constructed and the radiometric linear response capacity is test by adjusting electric gain, exposure time and radiance level. The linear polarizer and the sine function fitting algorithm are utilized to measure polarization effect. The integrating sphere calibration system is constructed in our Lab and its spectral radiance is calibrated by a well-characterized and extremely stable NIST traceable transfer spectroradiometer. Our manufactured convex grating imaging spectrometer is relative and absolute calibrated based on the integrating sphere calibration system. The relative radiometric calibration data is used to remove or reduce the radiometric response non-uniformity every pixel of imaging spectrometer while the absolute radiometric calibration is used to construct the relationship between the physical radiant of the scene and the digital number of the image. The calibration coefficients are acquired at ten radiance levels. The diffraction noise in the images can be corrected by the calibration coefficients and the uniform radiance image can be got. The calibration result shows that our manufactured imaging spectrometer with convex grating has 3.0% degree of polarization and the uncertainties of the relative and absolute radiometric calibrations are 2.4% and 5.6% respectively.
Noise equivalent temperature difference (NETD) is the key parameter characterizing the detectivity of infrared systems.
Our developed pushbroom longwave infrared imaging spectrometer works in a waveband between 8μm to 10.5 μm. Its
temperature sensitivity property is not only affected by atmosphere attenuation, transmittance of the optical system and
the characteristics of electric circuit, but also restricted by the self-radiation. The NETD accurate calculation formula is
derived according to its definition. Radiation analysis model of a pushbroom image spectrometer is set up, and its
self-radiation is analyzed and calculated at different temperatures, such as 300K, 150K and 120K. Based on the obtained
accurate formula, the relationships between the NETD of imaging spectrometer and atmospheric attenuation, F-number,
effective pixel area of detector, equivalent noise bandwidth and CCD detectivity are analyzed in detail, and self-radiation
is particularly discussed. The work we have done is to provide the basis for parameters determination in spectrometer
Modern star sensors are powerful to measure attitude automatically which assure a perfect performance of spacecrafts.
They achieve very accurate attitudes by applying algorithms to process star maps obtained by the star camera mounted
on them. Therefore, star maps play an important role in designing star cameras and developing procession algorithms.
Furthermore, star maps supply significant supports to exam the performance of star sensors completely before their
launch. However, it is not always convenient to supply abundant star maps by taking pictures of the sky. Thus, star map
simulation with the aid of computer attracts a lot of interests by virtue of its low price and good convenience. A method
to simulate star maps by programming and extending the function of the optical design program ZEMAX is proposed.
The star map simulation system is established. Firstly, based on analyzing the working procedures of star sensors to
measure attitudes and the basic method to design optical system by ZEMAX, the principle of simulating star sensor
imaging is given out in detail. The theory about adding false stars and noises, and outputting maps is discussed and the
corresponding approaches are proposed. Then, by external programming, the star map simulation program is designed
and produced. Its user interference and operation are introduced. Applications of star map simulation method in
evaluating optical system, star image extraction algorithm and star identification algorithm, and calibrating system errors
are presented completely. It was proved that the proposed simulation method provides magnificent supports to the study
on star sensors, and improves the performance of star sensors efficiently.
Spectral calibration of imaging spectrometer plays an important role for acquiring target accurate spectrum. There are two spectral calibration types in essence, the wavelength scanning and characteristic line sampling. Only the calibrated pixel is used for the wavelength scanning methods and he spectral response function (SRF) is constructed by the calibrated pixel itself. The different wavelength can be generated by the monochromator. The SRF is constructed by adjacent pixels of the calibrated one for the characteristic line sampling methods. And the pixels are illuminated by the narrow spectrum line and the center wavelength of the spectral line is exactly known. The calibration result comes from scanning method is precise, but it takes much time and data to deal with. The wavelength scanning method cannot be used in field or space environment. The characteristic line sampling method is simple, but the calibration precision is not easy to confirm. The standard spectroscopic lamp is used to calibrate our manufactured convex grating imaging spectrometer which has Offner concentric structure and can supply high resolution and uniform spectral signal. Gaussian fitting algorithm is used to determine the center position and the Full-Width-Half-Maximum（FWHM）of the characteristic spectrum line. The central wavelengths and FWHMs of spectral pixels are calibrated by cubic polynomial fitting. By setting a fitting error thresh hold and abandoning the maximum deviation point, an optimization calculation is achieved. The integrated calibration experiment equipment for spectral calibration is developed to enhance calibration efficiency. The spectral calibration result comes from spectral lamp method are verified by monochromator wavelength scanning calibration technique. The result shows that spectral calibration uncertainty of FWHM and center wavelength are both less than 0.08nm, or 5.2% of spectral FWHM.
The optical compressive spectral imaging method is a novel spectral imaging technique that draws in the inspiration of compressed sensing, which takes on the advantages such as reducing acquisition data amount, realizing snapshot imaging, increasing signal to noise ratio and so on. Considering the influence of the sampling quality on the ultimate imaging quality, researchers match the sampling interval with the modulation interval in former reported imaging system, while the depressed sampling rate leads to the loss on the original spectral resolution. To overcome that technical defect, the demand for the matching between the sampling interval and the modulation interval is disposed of and the spectral channel number of the designed experimental device increases more than threefold comparing to that of the previous method. Imaging experiment is carried out by use of the experiment installation and the spectral data cube of the shooting target is reconstructed with the acquired compressed image by use of the two-step iterative shrinkage/thresholding algorithms. The experimental result indicates that the spectral channel number increases effectively and the reconstructed data stays high-fidelity. The images and spectral curves are able to accurately reflect the spatial and spectral character of the target.
Compressive spectral imaging combines traditional spectral imaging method with new concept of compressive sensing thus has the advantages such as reducing acquisition data amount, realizing snapshot imaging for large field of view and increasing image signal-to-noise and its preliminary application effectiveness has been explored by early usage on the occasions such as high-speed imaging and fluorescent imaging. In this paper, the application potentiality for spatial coding compressive spectral imaging technique on rural survey is revealed. The physical model for spatial coding compressive spectral imaging is built on which its data flow procession is analyzed and its data reconstruction issue is concluded. The existing sparse reconstruction methods are reviewed thus specific module based on the two-step iterative shrinkage/thresholding algorithm is built so as to execute the imaging data reconstruction. The simulating imaging experiment based on AVIRIS visible band data of a specific selected rural scene is carried out. The spatial identification and spectral featuring extraction capacity for different ground species are evaluated by visual judgment of both single band image and spectral curve. The data fidelity evaluation parameters (RMSE and PSNR) are put forward so as to verify the data fidelity maintaining ability of this compressive imaging method quantitatively. The application potentiality of spatial coding compressive spectral imaging on rural survey, crop monitoring, vegetation inspection and further agricultural development demand is verified in this paper.
Imaging spectrometer is a promising remote sensing instrument widely used in many filed, such as hazard forecasting,
environmental monitoring and so on. The reliability of the spectral data is the determination to the scientific communities.
The wavelength position at the focal plane of the imaging spectrometer will change as the pressure and temperature vary,
or the mechanical vibration. It is difficult for the onboard calibration instrument itself to keep the spectrum reference
accuracy and it also occupies weight and the volume of the remote sensing platform. Because the spectral images suffer
from the atmospheric effects, the carbon oxide, water vapor, oxygen and solar Fraunhofer line, the onboard wavelength
calibration can be processed by the spectral images themselves. In this paper, wavelength calibration is based on the
modeled and measured atmospheric absorption spectra. The modeled spectra constructed by the atmospheric radiative
transfer code. The spectral angle is used to determine the best spectral similarity between the modeled spectra and
measured spectra and estimates the wavelength position. The smile shape can be obtained when the matching process
across all columns of the data. The present method is successful applied on the Hyperion data. The value of the
wavelength shift is obtained by shape matching of oxygen absorption feature and the characteristics are comparable to
that of the prelaunch measurements.
Hyperspectral imager is now widely used in many regions, such as resource development, environmental monitoring and so on. The reliability of spectral data is based on the instrument calibration. The smile, wavelengths at the center pixels of imaging spectrometer detector array are different from the marginal pixels, is a main factor in the spectral calibration because it can deteriorate the spectral data accuracy. When the spectral resolution is high, little smile can result in obvious signal deviation near weak atmospheric absorption peak. The traditional method of detecting smile is monochromator wavelength scanning which is time consuming and complex and can not be used in the field or at the flying platform. We present a new smile detection method based on the holmium oxide panel which has the rich of absorbed spectral features. The higher spectral resolution spectrometer and the under-test imaging spectrometer acquired the optical signal from the Spectralon panel and the holmium oxide panel respectively. The wavelength absorption peak positions of column pixels are determined by curve fitting method which includes spectral response function sequence model and spectral resampling. The iteration strategy and Pearson coefficient together are used to confirm the correlation between the measured and modeled spectral curve. The present smile detection method is posed on our designed imaging spectrometer and the result shows that it can satisfy precise smile detection requirement of high spectral resolution imaging spectrometer.
Compressive spectral imaging is a kind of novel spectral imaging technique that combines traditional spectral imaging method with new concept of compressive sensing. Spatial coding compressive spectral imaging realizes snapshot imaging and the dimension reduction of the acquisition data cube by successive modulation, dispersion and stacking of the light signal. It reduces acquisition data amount, increases imaging signal-to-noise ratio, realizes snapshot imaging for large field of view and has already been applied in the occasions such as high-speed imaging, fluorescent imaging and so on. In this paper, the physical model for single dispersion spatial coding compressive spectral imaging is reviewed on which the data flow procession is analyzed and its reconstruction issue is concluded. The existing sparse reconstruction methods are investigated and specific module based on the two-step iterative shrinkage/thresholding algorithm is built so as to execute the imaging data reconstruction. A regularizer based on the total-variation form is included in the unconstrained minimization problem so that the smooth extent of the restored data cube can be controlled by altering its tuning parameter. To verify the system modeling and data reconstruction method, a simulation imaging experiment is carried out, for which a specific imaging scenery of both spatial and spectral features is firstly built. The root-mean-square error of the whole-band reconstructed spectral images under different regularization tuning parameters are calculated so that the relation between data fidelity and the tuning parameter is revealed. The imaging quality is also evaluated by visual observation and comparison on resulting image and spectral curve.
The developed spaceborne camera is an exclusive functional load of a micro satellite.
The signal-to-noise ratio (SNR) reflects its radiance response and is the parameter that directly
associates with the quality of its acquired images. The SNR determination task of the spaceborne
camera mainly consists of two parts: As is reported before firstly the spatial environment is
simulated and the atmosphere transmission mode is built with MODTRAN to calculate and predict the SNR of the speceborne camera under aerial working condition. In this paper, the in-lab measuring experiment is carried out to measure the theoretical imaging performance of the camera before its aerial use. An integrating sphere is utilized to supply well-proportioned illumination, and a number of images are acquired by the spaceborne camera under different luminance conditions. The images are processed in use of certain algorithm and a special filter to extract the noise. The SNRs corresponding to different illumination conditions are calculated so that full-scale radiance response feature of the camera can be gained. The dynamic range is another parameter that characterizes the imaging capacity of a camera. The relationship between dynamic range and SNR of a camera is to be explored in this paper. Different dynamic configurations are set and the SNRs of different dynamic range configurations are tested, which experimentally reveals the dynamic range's influence on SNR.
The signal processing flow for the MTF test bench that is based on Fourier analysis method is
The signal processing flow mainly consists of three parts that are Fourier analyzing, background
correction and system attenuation elimination. The center of the pinhole area is recognized
automatically and the line spread functions (LSF) of both sagittal and tangential directions are
calculated. Second-order fast Fourier transform is executed so that a primary two-direction MTF result
is gained. Either auto Fourier-domain background correction or manual time-domain background
correction is executed. The attenuation of the tested MTF result due to the influence of the detector and
pinhole is eliminated finally.
A commercially available 50-mm plano-convex audit lens is tested as the sample to validate the
accuracy of the signal processing flow of the MTF test bench. The test error is below 0.01 under
A real-time MTF test bench for visible optical systems is presented in this paper. This test bench can perform quick
on-axis and off-axis MTF measurement of optical systems whose aperture are less than 200mm in visible wavelength. A
high quality off-axis parabolic collimator is used as object generator of this test bench. The image analyzer is a
microscopy with CCD camera installed on a multi-axis motion stage. The software of this MTF test bench provides a
good interface for the operators to set measurement parameters and control this bench. Validation of this test bench,
performed with a 50mm plano-convex audit lens, shows that MTF measurement error of this bench is within 0.04.
Besides MTF measurement, this bench can also perform effective focal length (EFL) and back focal length (BFL)
without any hardware modification. Transmittance of optical system can also be performed on this bench with an
Modulation Transfer Function (MTF) is the spatial frequency response of imaging systems and now develops as an
objective merit performance for evaluating both quality of lens and camera. Slanted-edge method and its principle for
measuring MTF of digital camera are introduced in this paper. The setup and software for testing digital camera is
respectively established and developed. Measurement results with different tilt angle of the knife edge are compared to
discuss the influence of the tilt angle. Also carefully denoise of the knife edge image is performed to decrease the noise
sensitivity of knife edge measurement. Comparisons have been made between the testing results gained by slanted-edge
method and grating target technique, and their deviation is analyzed.
Star camera is a kind of sensitive attitude sensors used for navigation of space vehicles. In order to use it on aircrafts in
daytime, the conceptual design and the principle of airborne daytime infrared star cameras are introduced in this paper, as
there is enough number of stars in near infrared band to be used as reference of a star camera for calculating attitude.
Through analyzing the atmospheric scattering background light intensity for different altitudes, observing angles, and
solar angles with Modtran software, and considering IR FPA (infrared focal plane array) performance, shot noise and the
required star magnitude for daytime star trackers and sensors, the optical system parameters, i.e. FOV (field of view),
clear aperture diameter and effective focal length, are determined according to the required SNR (signal to noise ratio).
Proc. SPIE. 7658, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronic Materials and Devices for Detector, Imager, Display, and Energy Conversion Technology
KEYWORDS: Hyperspectral imaging, Imaging systems, Cameras, Data storage, Image processing, Spectroscopy, Photography, Imaging spectroscopy, Digital micromirror devices, Astronomical imaging
The primary compact high resolution imaging spectrometer was developed and reported. Due to
its numerous wave bands the original image data is always in a huge scale and costs a tremendous
process overhead, but the data amount of the region of interest is as a rule in the order of thousandth, if
not less, of that of the whole push-broom region. With a digital micromirror device (DMD), only the
region of interesting object is imaged by the imaging spectrometer, which results in a distinct reduction
of data quantity and a high data compression ratio.
A DMD of high turning rate and residential time adjustability is used as a spatial light modulator
to fulfill the object selection function. It is placed after the fore objective and able to reflect the object
to either the panchromatic CCD camera channel or the imaging spectrometer channel. The position of
the object can be firstly determined through the image interpretation from panchromatic imaging
channel and a DMD control command is executed to switch the corresponding mirrors to the imaging
spectrometer channel, thus only the object region of interest is imaged by the spectrometer.
The multiple objects of both printed patterns and real leaves are accurately determined and
selected according to their different locality and shape features. The panchromatic and hyperspectral
image data are both collected for further effective object recognition.
The requirement for low distortion in either spatial or spectral direction of a push-broom imaging
spectrometer has been recently recognized. Though distortion scale of as much as 1 or 2 pixels have
been accepted in previous spectrometer designs, it is suggested to be limited to the order of hundredth
of a pixel to preserve the validity and integrity of the spectral imaging data.
The developed push-broom imaging spectrometer adopts a reflective Offner relay structure and
provides good optical correction and compact size. The spectral and spatial distortion measurement is
of significance for instrument performance evaluation and alignment guidance. In this paper, two
easy-to-implement and effective measurement methods for both spatial and spectral distortion are
By using a standard Hg-Cd lamp as both the illuminating source and the object, the spectroscopic
image of the slit focusing onto the CCD focal plane is collected. In certain rows of the image, the
center positions of every spectral line are recorded. Through the comparison of recorded positions of
different rows, the spectral line bending of the calibrated imaging spectrometer is worked out.
In the continuous spectrum illumination condition and by using a self-made mask as the object,
the entrance slit image is cut into tens of tiny rows that correspond to different image heights. The
center positions of 5 typical rows are calculated and five chromatic distortion curves are worked out
with certain interpolation method.
After alignment of an imaging spectrometer, the image of a special wavelength should in theory
strictly meet with the design value and is focused on a certain column of the CCD focal plane. Since
the imaging spectrometer is usually used in spatial or aerial environment, the optical components and
the detector will departure from the regulated place and leads to focusing the image onto the deflected
position of the focal plane in the spectral direction.
Since the onboard readjustment of an inaccurate imaging spectrometer is usually unavailable, the
equivalent task should be performed by certain post processing method. In this paper, we present a
wavelength calibration method based on a fitting algorithm. Because of the linear diffraction feature of
a grating, first order fit is adopted for the calibration. Using a standard mercury lamp as the light source
during the calibration, the experimental imaging data collected from the whole CCD focal plane is used
for the wavelength calibration to construct the actual wavelength distributing curve.
Because of spectral line bending (smiling) of the imaging spectrometer, the wavelength calibration
result of each row of the CCD plane differs so that a row-by-row calibration work should be carried out.
The total row-by-row calibration result not only provides a full-scale and high-precision calibration
effort, but also brings forward a smiling evaluation method for the whole imaging spectrometer.
Using a standard Hg-Cd lamp as both the illuminating light source and the object, the
spectroscopic image of the slit focusing onto the CCD focal plane of a calibrated imaging spectrometer
is collected. In certain rows of the image, the center position of every spectral line is recorded. Through
the comparison of recorded positions of different rows, the smiling of the calibrated imaging
spectrometer is worked out, which meets with the design value.
Thermal environment adaptability is an important aspect which should be involved in the development and test of a
space camera. Generally, vacuum thermal test and thermal cycle test are two important thermal tests to ensure the
reliability of a space camera. In this paper, vacuum thermal test and thermal cycle test of a space camera are introduced.
During the test, we check if the camera can work normally and evaluate performance of the camera under different
temperature. The performance is evaluated by the modulation transfer function (MTF) of the camera. According to the
measured MTF curve, the influence of temperature on performance of this camera is evaluated.
The aerospace camera developed is an exclusive functional load of a micro satellite. The
signal-to-noise ratio of the aerospace camera reflects its radiance response and is the parameter that
directly associates with the quality of its acquired images. The traditional way to calculate the
signal-to-noise ratio of a camera is to substitute the related parameters of its subassemblies into the
deduced formulas. This kind of method lacks the focalization on the diversities of its components and
specific application occasions. The result tested by using standard uniform source can certainly be
utilized to evaluate the work performance of the camera, but it ignores its actual orbital atmospheric
condition and consequentially leads to unavoidable data deviation.
The atmospheric transmission model is built and the radiation condition of the aerospace camera
in orbit is simulated by means of MODTRAN. Instead of building the noise model based on electronic
devices of the camera to get theoretical noise data, considering the difference of the noises of the
camera between in-lab and on-orbit condition, we adopt the measured noise data of the CCD camera to
calculate the signal-to-noise ratio so as to make it approach the real value as possible.
The influences of the changes of solar altitude angle, earth surface albedo and weather condition
on the signal-to-noise ratio of the camera are quantitatively determined. The result of the
signal-to-noise ratio can be used as the basis to evaluate the remote sensing imaging quality and to
decide the feasible exposure time.
The 3-5μm wave length region has been recognized as an effective mid infrared spectral range for the detection of high
temperature events on Earth surface with remote sensing camera. Most of current mid infrared remote sensors relied on
cooled detectors. Although they have high radiometric sensitivity, they inevitably are large size and weight, high power
consumption, short life-time, and high cost. With the advent of uncooled thermal detectors, the miniaturization of mid
infrared imagers suitable for microsatellite is being investigated widely. Based on uncooled focal plane array, a
conceptual compact midwave infrared sensor has been put forward. It is designed for hot spot detection. First, working
environments and requirements of the sensor for hot spot detection is introduced. Then the characteristic of its main
constituent parts including selected uncooled focal plane array and the designed optical system is presented. Because
uncooled focal plane array has lower radiometric sensitivity than the cooled, we are more concerned about the thermal
resolution of the system. And its performance including sub-pixel hot spot detection capabilities and spatial resolution is
evaluated. It shows that the suggested compact sensor with uncooeld focal plane array can not meet the requirement.
The remote camera that is developed by us is the exclusive functional load of a micro-satellite.
Modulation transfer function (MTF) is a direct and accurate parameter to evaluate the system
performance of a remote camera, and the MTF of a camera is jointly decided by the MTF of camera
lens and its CCD device. The MTF of the camera lens can be tested directly with commercial optical
system testing instrument, but it is indispensable to measure the MTF of the CCD device accurately
before setting up the whole camera to evaluate the performance of the whole camera in advance.
Compared with other existed MTF measuring methods, this method using grating pattern requires less
equipment and simpler arithmetic. Only one complete scan of the grating pattern and later data
processing and interpolation are needed to get the continuous MTF curves of the whole camera and its
CCD device. High-precision optical system testing instrument guarantees the precision of this indirect
measuring method. This indirect method to measure MTF is of reference use for the method of testing
MTF of electronic device and for gaining MTF indirectly from corresponding CTF.
The remote camera developed by us is the exclusive functional load of the micro-satellite. The
remote camera is based on the frame transfer CCD sensor DALSA FT18, and for the purpose of
insuring system reliability, the development of the remote camera indispensably simplifies the design
of mechanical and electrical shutter, which causes the problem of CCD smearing in remote sensors, and
leads to the distortion of remote sensing images. In this paper we present a reversely stepwise method
to solve the CCD smearing problem in remote sensors. The images retrieved from data after correction
show great improvement in image contrast and quality.