Conference PaperPDF Available

Visible and near-infrared imaging spectrometer (VNIS) for in-situ lunar surface measurements

Authors:

Abstract and Figures

The Visible and Near-Infrared Imaging Spectrometer (VNIS) onboard China’s Chang’E 3 lunar rover is capable of simultaneously in situ acquiring full reflectance spectra for objects on the lunar surface and performing calibrations. VNIS uses non-collinear acousto-optic tunable filters and consists of a VIS/NIR imaging spectrometer (0.45–0.95 μm), a shortwave IR spectrometer (0.9–2.4 μm), and a calibration unit with dust-proofing functionality. To been underwent a full program of pre-flight ground tests, calibrations, and environmental simulation tests, VNIS entered into orbit around the Moon on 6 December 2013 and landed on 14 December 2013 following Change’E 3. The first operations of VNIS were conducted on 23 December 2013, and include several explorations and calibrations to obtain several spectral images and spectral reflectance curves of the lunar soil in the Imbrium region. These measurements include the first in situ spectral imaging detections on the lunar surface. This paper describes the VNIS characteristics, lab calibration, in situ measurements and calibration on lunar surface.
Content may be subject to copyright.
Visible and Near-Infrared Imaging Spectrometer (VNIS) For In Situ Lunar
Surface Measurements
Zhiping He, Rui Xu, Chunlai Li, Gang Lv, Liyin Yuan, Binyong Wang, Rong Shu, Jianyu Wang
Key Laboratory of Space Active Opto-Electronics Technology, Shanghai Institute of Technical Physics, Chinese
Academy of Science, Shanghai, China
ABSTRACT:
The Visible and Near-Infrared Imaging Spectrometer (VNIS) onboard China’s Chang’E 3 lunar rover is capable of
simultaneously in situ acquiring full reflectance spectra for objects on the lunar surface and performing calibrations.
VNIS uses non-collinear acousto-optic tunable filters and consists of a VIS/NIR imaging spectrometer (0.45–0.95
μm), a shortwave IR spectrometer (0.9–2.4 μm), and a calibration unit with dust-proofing functionality. To bee n
underwent a full program of pre-flight ground tests, calibrations, and environmental simulation tests, VNIS entered
into orbit around the Moon on 6 December 2013 and landed on 14 December 2013 following Change’E 3. The first
operations of VNIS were conducted on 23 December 2013, and include several explorations and calibrations to
obtain several spectral images and spectral reflectance curves of the lunar soil in the Imbrium region. These
measurements include the first in situ spectral imaging detections on the lunar surface. This paper describes the
VNIS characteristics, lab calibration, in situ measurements and calibration on lunar surface.
Keywords: space vehicles: instruments, instrumentation: spectrographs, Moon, techniques: spectroscopic,
1. INTRODUCTION
Chang’E 3 operated by the China National Space Administration (CNSA) is the third in the Chang’E program
and consists of a lunar surface Lander and a lunar Rover, which is known as Yutu (meaning ‘jade rabbit’) 1–3.The
Visible and Near-infrared Imaging Spectrometer (VNIS) is one of the main scientific payloads on Yutu and consists
of an imaging spectrometer (0.45-0.95μm), a spectrometer (0.9-2.4μm), and a calibration unit. it is mounted on
the front of the rover to detect lunar surface objects with a 45° viewing angle and obtain the spectra and geometry
data at a height of 0.69 m4–7.
Minerals such as pyroxene, plagioclase, olivine, and ilmenite, which constitute most of lunar surface rocks with
varying size and shape, have distinctive spectral characteristics in the VNIR and SWIR regions, as shown in fig 14.
Morphological measurements and spectral measurements are the two main methods for analyzing rock structure and
composition. An imaging spectrometer has the ability to simultaneously obtain both the images and the spectral
signatures of the targets in the scene, and is widely used in terrestrial and space-based remote sensing applications.
The VNIS mostly addresses lunar surface material composition and available resource exploration. Mounted on the
platform of lunar rover Yutu, the VNIS detects the spectra and images of lunar objects in the roving area to provide
scientific data for determining the lunar surface mineral composition and performing comprehensive analysis of the
chemical composition5.
Sensors, Systems, and Next-Generation Satellites XIX, edited by Roland Meynart, Steven P. Neeck, Haruhisa Shimoda
Proc. of SPIE Vol. 9639, 96391S · © 2015 SPIE · CCC code: 0277-786X/15/$18 · doi: 10.1117/12.2194526
Proc. of SPIE Vol. 9639 96391S-1
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
08
02
- olivinediopside
M1vpersM1ene
umerele
00400 800 1200 1688
wavelength /nm 2000 2400
The calibration and
dustproof components
The non- worlung
status
Calibration
ode r5
Spectral
imaging mode
45° (the solar elevation angle)
The lunar surface
L
rCalibration
Unit
electronics
C
Collimating Lens VNHOiF
ino
C
Field
Diaphragm Imaging Lens
Area Array CMOS I Ci
VIS object! WW
Aelectronics ">
JW
IR obi iv T
mcaAS Detector COE
Field
Diaphragm [ Imaging Lens J
[ Collimating Lens > IRAOTF
RF Driver
electronics
The clothing
Board of base
The installation base
CPU
The calibration and
dust -proof components
Fig.1 The spectral reflectance curves of main single minerals of lunar surface (left) and the VNIS onboard Rover (right)
2. VNIS
The VNIS is designed for the scientific exploration mission of identifying the material composition and
available resources over the roving area of the lunar surface.As a passive optical instrument, the VNIS measures the
radiance diffusely reflected from solar illumination of the Moon’s surface. The VNIS use non-collinear AOTFs as
dispersive devices, and it has two detection channels: a VIS/NIR channel (0.45–0.95 μm) with a CMOS area array
detector, and a SWIR channel (0.9–2.4 μm) with an InGaAs single-element detector. It includes image-forming lens,
collimating lens, AOTF(acousto-optic tunable filter) light-splitting component, convergent lens, the detector
component, motor drive, RF(Radio Freqency) drive and main control circuit, as is shown in Fig24.
Fig.2 Overview of the VNIS system
Proc. of SPIE Vol. 9639 96391S-2
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
1=10.. -
11.=1,
The working principle of the VNIS is briefly described as follows5-7: reflected light from lunar objects arrives at
the AOTFs, where only narrow-wavelength-band data or imaging information passes through, depending on the
frequency that the RF driver generates. Then, the quasi-monochromatic light converges on the detector. The
spectrometer can realize flexible and rapid wavelength selection by altering the driving frequency exerted on the
AOTF, so we can acquire spectra or image data at different wavelengths over the available spectral coverage.
The VNIS adopted a splitting design that consists of a spectrometer probe located outside of the rover, and a
logical control and AOTF radio-frequency (RF) driver module, which is a unit called Remote Electric Control Box,
located inside the rover. These two parts are connected by cables and the configuration of the VNIS instrument is
shown in Fig.36.The major technical specifications of the VNIS are shown in Table 15–7.
Table 1 Main performance specifications of VNIS
Description
Specification
V-NIR SWIR
Spectral coverage (nm) 450-950 900-2400
Spectral resolution (nm) 2-7 3-12
FOV (degree) 8.5×8.5 Φ3.6
Effective pixels 256×256 1
Quantization (bits) 10 16
SNR(dB) 31 32
Spectral sampling interval (nm) 5
Power consumption (W) 19.8
Weight(kg)
4.7 (Spectrometer probe)
0.7 (Logical control component in RECB)
Fig.3 Spectrometer probe of VNIS (left) and Remote Electrical Control Box (right).
The VNIS consists of a VNIR imaging channel and SWIR spectral channel. Their optical systems are both
composed of: an objective lens, field diaphragm, collimating lens, AOTF, imaging lens and detector, as shown in
Fig46.The VNIR channel and the bases of the SWIR channel’s image-forming mirrors lay on the main optical
backplane, while other parts of the SWIR channel are mounted on a lateral optical backplane.
Proc. of SPIE Vol. 9639 96391S-3
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
SWIR Objectiv VNIR Objective Mirror
Collimating Lens
Lens
'SWIR
AOTF
Single Element Detector
Detector Array
vN IRImaging Lens
The VNIS has the following functions6-7:
1) obtain spectral image data on specified objects in the visible and NIR (0.45–0.95 μm) and spectral data on
specified objects in the SWIR (0.9–2.4 μm)
2) obtain reflectance spectral images in the visible and NIR and reflectance spectra in the SWIR
3) perform on-orbit calibration
4) provide dust-proofing and insulation.
The calibration unit performs the calibration function and consists of an ultrasonic motor, framework, and an
internal diffuser panel. The inner surface of the calibration unit is the diffuser panel, which is located at the light
entrance. When the spectrometer is operated in detection mode, the calibration unit can be completely open at a 55°
angle to the mounting plane, which does not affect the light entrance. When the spectrometer operated in calibration
mode, the solar spectral irradiance was used as a calibration source, and the diffuser panel of calibration unit lay
parallel to the mounting plane to obtain calibration data. When it was not working, the calibration unit could be
closed up within the framework to prevent spectrometer damage from dust and other pollution and also to provide
good thermal insulation6-7.
Fig.4 Schematic diagram of the optical mudule
Proc. of SPIE Vol. 9639 96391S-4
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
W6 An.rn L CIozBC
Fig.5 Detection, calibration, and dust-proofing scheme of VNIS.
3. MAIN CHARACTERISTICS
The VNIS can obtain a spectral image in the VIS/NIR band and spectral data in the SWIR band simultaneously.
Its main characteristics include spectral characteristics, radiometric response characteristicsdata characteristics, etc.
3.1 Spectral Characteristics
The spectral range and resolution of the VNIS are key characteristics and indicators for achieving the scientific
objectives and are directly related to the instrument’s ability to identify minerals by their spectra. AOTF is
dispersive component and has a direct impact on the final measurements of the spectrometer11. Its parameters, such
as the relation between diffraction wavelengths, RF driving frequency, diffraction efficiency, and spectral resolution,
should be tested before system integration and calibration. The AOTF performance analysis system is designed to
test the parameters of the AOTFs. Then, corresponding formulae for wavelength and RF driving frequency are fitted
using five order polynomials as the initial data for the instrument’s spectral calibration5, 11.
In the laboratory spectral calibration, the combination of a narrowband monochromatic source (including a
narrowband laser and monochromator) and a small passive integrating sphere was used as a light source, which is
shown in Fig.6. After calibration on the ground and confirmation of the calibration, the spectral range of the VNIS is
450–2400 nm, and the spectral resolution is 2–12 nm. The spectral resolutions are 2–7 nm in the VIS/NIR band and
3–12 nm in the SWIR band, as shown in Fig.74-7.
Proc. of SPIE Vol. 9639 96391S-5
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
AOTF
Imaging
Spectrometer
Narrowband
Monochromatic
Source
Response curve of 487.0 nm Laser source
1000
900
800
700
600
ó500
400
300
200
100
Peak wavelength @ 487.1nm
X: 487.1
Y: 505
0475 480 485 490 495 500
wavelength nm
Fig.6 Configuration of laboratory spectral calibration and calibration curve
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
0
2
4
6
8
10
12
wavelength (nm)
FWHM (nm)
V-NIR c hannel of VNIS
SWIR channel of VNIS
Fig.7 Spectral resolution of VNIS
3.2 Radiometric Characteristics
Radiometric calibration is a procedure that associates the value measured by the instrument [e.g., the data
number (DN) of a CMOS image pixel or single-element detector] with absolute physical quantities (such as the
spectral radiance). The inversion model for the radiance of a target is established using a standard radiation source.
The configuration of the laboratory radiometric calibration system is shown in Fig.8; the radiance level of the
integrating sphere can be adjusted by switching the calibrated lamps6.
Proc. of SPIE Vol. 9639 96391S-6
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
H910ä6 lnua21
Pwk
vonllAJiilll
?bps
Fig.8 Configuration of laboratory radiometric calibration system
The spectrometer probe of VNIS instrument is aimed at the central area of the integrating sphere port, where
the uniformity is better than 1‰. The DN curves, (, )
D
NClass
λ
, were acquired by VNIS under different integrating
sphere radiance levels calibrated as (, )IsRad level
λ
. The radiance inversion model is shown in Eq. (1)6.
,, 0,
,, 0,
(, ) ( (, )) (, )
(, ) ( (, ) (, ))
ij ij ij
ij ij ij
DN Class f IsRad level DN Class
I
sRad level g DN Class DN Class
λ
λλ
λλλ
=+
=−
(1)
Where pixel (, )ijcan be ignored in the SWIR channel since the SWIR detector has only a single element.
,(, )
ij
D
NClass
λ
is the DN response curve of the SWIR single element detector or each pixel (, )ijon the CMOS
detector under certain operating modes, while 0, (, )
ij
D
NClass
λ
is the corresponding dark level curve. The response
matrix of available signal of the detectors is ,()
ij
f, while ,()
ij
g is the corresponding inverse matrix. For VNIS, the
radiance inversion model is calculated based on the radiometric calibration results through a linear model6.
In radiometric calibration, the spectral response data are acquired under different integrating sphere radiance
levels. Therefore, the radiance inversion model is finally obtained by linear fitting to the DN of each pixel in each
band with the trend of the variation in the light source. The uncertainty of the inversion results is 3.69% in the
VIS/NIR channel and 5.39% in the SWIR channel5-7.
The signal-to-noise ratio (SNR) is an important indicator of the radiometric response characteristics of the
VNIS and changes with the input signal when the noise is fixed. The SNR of the VNIS was tested and analyzed by
ground radiometric calibration, and the SNR was obtained by calculation as shown in Fig.9.When the albedo is 0.09
and the solar elevation angle is 45° in the VIS/NIR band, and the albedo is 0.09 and the solar elevation angle is 15°
in the SWIR band, the SNR must be greater than 30 dB7.
Proc. of SPIE Vol. 9639 96391S-7
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
0
50
100
150
200
wavelength / nm
S/N
S/N of VIS/NIR channel
S/N of SWIR channel
40 dB
30 dB
Fig.9 SNR of VNIS
While operating on the lunar surface, the VNIS is required to obtain reliable data over a large temperature range,
from –20° to 55°. Furthermore, due to the splitting design of VNIS instrument, the spectrometer probe and RECB
are in environments with different temperatures. A series of tests were designed in order to determine the influence
of temperature fluctuations on the SWIR channel that is more temperature sensitive. First of all, the standard
temperature curves of the RF amplifier and the InGaAs detector, with the thermoelectric cooler (TEC) at room
temperature (23±1°C), were measured as a reference. Then, a detection system was set up, using an integrating
sphere as an active radiation source and a vacuum tank as the temperature regulator. The temperature characteristics
of the spectrometer probe and RECB were analyzed independently and the temperature effect correction models for
the RF amplifier and the detector were modeled6.
3.3 DATA CHARACTERISTICS
The VNIS is equipped with a VIS/NIR spectral imaging channel and SWIR spectral detecting channel with an
18 mm separation between the optical axes; these systems can detect lunar surface objects simultaneously. With a
spectral sampling interval of 5 nm, the VNIS detected the lunar surface default automatically, and it sequentially
sampled 100 frames of spectral images in the VIS/NIR band and 300 frames of spectral data in the SWIR band. In
addition, two spectral bands each obtained an extra 20 frames of dark level for data processing. The geometrical
characteristics of imaging in the VIS/NIR band and spectral detection in the SWIR, as obtained by testing and
calibration on the ground, are shown in Figure 10. The circle represents the SWIR channel’s field of view (FOV),
which has a diameter of 107 pixels and is centered at the coordinate (96, 128) of the VIS/NIR channel4.
The specific order of data detection by the VNIS is5-6:
1) sampling 10 frames of dark level data in the VIS/NIR band (CMOS array detector);
2) sampling 10 frames of dark level data in the SWIR band (InGaAs single-element detector);
3) obtaining 300 frames of scientific detection data from the lunar surface (in detection mode) or the calibration
diffuse reflection plate (in calibration mode) in the SWIR band (InGaAs single-element detector);
4) sampling 10 frames of dark level in the SWIR band (InGaAs single-element detector);
Proc. of SPIE Vol. 9639 96391S-8
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
o, o255, 0
0, 255
The pixel in the center of
SWIR channel FOV is
( 96, 128), and the
diameter is 107 pixels.
255, 255
CMOS Detector
Level 1 Data
Subtracti
Flat Field
VNIS Raw
Data
SWIR Detector
Level 1 Data
Dark
Current
Subtraction
Temperature
Calibration
CMOS Detector
Level 2A Data
tic
Calibration
Radiometri
Calibratio
Geometric
Cal ibratioli
SWIR Detector
Level 2A Data
Geometric
Calibration
CMOS Detector
Level 2B Data
SWIR Detector
Level 2B Data
5) sampling 100 frames of scientific detection data in detection mode or calibration mode in the VIS/NIR band
(CMOS array detector);
6) sampling 10 frames of dark level in the VIS/NIR band (CMOS array detector).
Fig.10 Geometrical relationships in VNIS detection
Fig.11 Preprocessing pipeline and data products for VNIS data
The images and spectral data obtained in detection and calibration modes were the original light response
signals, which should be used after data preprocessing and scientific data processing were completed. The data
preprocessing applied to the raw data included dark current deduction and temperature, radiometric, and geometric
corrections. As VNIS is the first AOTF type imaging spectrometer to be used for lunar exploration, its instrument
preprocessing is shown in Fig.118. The instrument data preprocessing pipeline mainly contains channel data
preprocessing and SWIR channel data preprocessing for the two different detectors.
Proc. of SPIE Vol. 9639 96391S-9
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
19`30'48"W 19`3047"1N 19°3046"W 19°30'45"W 19°30'
andér
* Finished Exploration Points
Navigation Points
Rover Rotite
19 °30'48"W
N0209(17,61)
I.
208(16,N)
90207(15,N)
)NO2C4(12,N)
19`30'43"W 19`30'42"W
N01039,801
0104(4,0) 1
14,
I
N0108(8.E2/83/H)
,;N0201(9,N)
'1_^-1,E1)
/19°30'4]"W 19°30'46"W 19°30'45"W 19°30'44"W 19'30'43"W 19°30'42"W
,
0.15
0.12 -
0.09 -
0.06 -
0.03 -
- Node_E_Reflectance
- Node_S3_Reflectance
- Node_N203_Reflectance
- Node N205 Reflectance
tit t
500 1000 1500 2000 2500
Wavelength(nm)
4. Data Acquisitions
The VNIS has two operating modes for working on the lunar surface: lunar surface detection, and in-orbit
calibration. In detection mode, the spectrometer begins to collect data of lunar surface; in calibration mode, the
spectrometer uses solar radiation as its calibration source. Here, the diffuser panel of the calibration unit is set to the
horizontal position to detect the solar radiance. By injecting instruction codes, the VNIS can shift the operating
modes to detection or calibration4.
Fig. 12 Map of the path traversed by the Yutu rover and the distribution of detection points
Fig.13 Data from VNIS: false color picture (500 nm, 550 nm, 645 nm, right) and spectral reflectance curves
After the Chang’E 3 mission began the scientific exploration stage, the VNIS instrument successfully
Proc. of SPIE Vol. 9639 96391S-10
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
completed the first lunar surface spectral acquisition at BTC 10:10 on Dec. 23rd, 2013. After the first two lunar days,
VNIS made measurements at four different points (E, S3, N203 and N205 in Fig. 12), and obtained data in detection
mode four times and calibration mode three times. The total size of data is 350 MB. All these data have been
released to the scientific community8.
5. CONCLUSION
As the main scientific payload of the Chang’E 3 rover, the VNIS completed a ground test, calibration, and
environmental simulation test. After landing successfully on the Moon, the VNIS performed several explorations and
calibrations, and obtained several spectral images and spectral reflectance curves of the lunar soil in the Imbrium
region following its first successful operation on the Moon on December 23, 2013. The VNIS performed the first
in-situ spectral imaging detection on the lunar surface; the high-resolution and informative spectral imaging data
obtained by the VNIS can provide a more valuable reference for scientific applications4-7.
Acknowledgments
This paper was supported by the Chinese lunar exploration program’s special funds for the second phase and the National Natural
Science Foundation (No. 21105109). The authors thank the Science and Application Center for Moon and Deep Space
Exploration of the Chinese Academy of Sciences for the ground test and data preprocessing, and the National Space Science
Center of the Chinese Academy of Sciences for its contributions to the development and testing of the instruments.
References
[1] Ye, P. J. and Peng, J., “Deep space exploration and its prospects in China,” Eng. Sci. 5(1), 1-5 (2008).
[2] Dai, S. W., Jia, Y. Z., and Zhang, B. M., “Chang’E-3 scientific payloads and its checkout results,” Sci. Sin. Tech. 44(4),
361-368 (2014).
[3] Ouyang, Z. Y., “Scientific objectives of Chinese Lunar Exploration Project and Development Strategy,” Adv. Earth Sci.
19(3), 351-358 (2004).
[4] He, Zh., Wang, B., Lv, G., Li, Ch., Yuan, L., Xu, R., Chen, K., and Wang, J., Visible and Near-Infrared Imaging
Spectrometer (VNIS) and Its Preliminary Results from the Chang’E 3 ProjectRev. Sci. Instrum., 86,8 (2014).
[5] He, Zh., Wang, B., Lv, G., Li, Ch., Yuan, L., Xu, R., Chen, K., and Wang, J., Visible and Near-infrared Imaging
Spectrometer (VNIS) for Chang’E-3”, Proc. SPIE 9263, 92630D-1 (2014).
[6] J. Wang, Z. He, R. Shu, R. Xu, K. Chen, and C Li, “Visible and Near-infrared Imaging Spectrometer aboard Chinese
Chang’E-3 Spacecraft”, Ch. 5 in Optical Payloads for Space Missions, S-E Qian, Ed., ISBN:9781118945148, John Wiley &
Sons (2015)
[7] Zhi-Ping He, Bin-Yong Wang, Gang Lv, Chun-Lai Li, Li-Yin Yuan, Rui Xu, Bin Liu, Kai Chen and Jian-Yu Wang,
“Operating principles and detection characteristics of Visible and Near-Infrared Imaging Spectrometer (VNIS) in Chang’e 3”,
Res. Astron. Astrophys. 14(12), 1567 (2014).
[8]Bin Liu, Chun-Lai Li, Guang-Liang Zhang, Rui Xu, Jian-Jun Liu, Xin Ren,Xu Tan, Xiao-Xia Zhang, Wei Zuo1 and
Wei-Bin Wen,Data processing and preliminary results of the Chang’e-3 VIS/NIR Imaging Spectrometer In-situ Analysis”,
Res. Astron. Astrophys. 14(12), 1578 (2014).
Proc. of SPIE Vol. 9639 96391S-11
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
[9] He, Z. P., Shu, R., and Wang, J. Y., “Imaging spectrometer based on AOTF and its prospects in deep-space exploration
application,” Proc. SPIE 8196, 819625 (2011).
[10] Gupta, N., “Acousto-optic tunable filters for infrared imaging,” Proc. SPIE 5953, 59530O (2005).
[11] Xu, R., He, Z. P., Zhang, H., Ma, Y. H., Fu, Z. Q., and Wang, J. Y., “Calibration of imaging spectrometer based on
acousto-optic tunable filter (AOTF),” Proc. SPIE 8527, 85270S (2012).
[12] Liu, B., Liu, J., Zhang, G., Ling, Z., Zhang, J., He, Zh., Yang, B., and Zou, Y., “Reflectance conversion methods for the
VIS/NIR imaging spectrometer aboard the Chang'E-3 lunar rover: based on ground validation experiment data,” Res. Astron.
Astrophys. 13(7), 862 (2013).
Proc. of SPIE Vol. 9639 96391S-12
Downloaded From: http://spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
... The VNIS is one of the main scientific payloads on the lunar rovers for Chang'e 3 and Chang'e 4. It uses AOTFs as the dispersive components. 10,11 The VNIS mostly addresses the lunar surface material composition and available resource exploration for determining the lunar surface mineral composition and performing a comprehensive analysis of the chemical compositions. The VNIS is mounted on the platform of the lunar rover and detects the spectra and images of the lunar objects in the roving area to provide scientific data. ...
... The operating modes and dust-proofing function were realized by the self-locking characteristics of the USM. 10 The structure and function of the calibration unit are shown in Fig. 6. The VNIS was mounted in front of the lunar rover to detect lunar surface objects at a 45-deg viewing angle and to obtain the spectra and geometric data at a height of 0.695 m, as shown in Fig. 7. ...
... The SNR is >31 dB in the VIS-NIR band when the albedo is 0.09 and the solar incident angle is 45 deg; and the SNR is >32 dB in the SWIR channel when the albedo is 0.09 and the solar incident angle is 75 deg. 10 The main performance specifications of the VNIS are shown in Table 3. ...
... On the first two lunar days, the CE-3 Yutu rover carried the VNIS, which obtained measurements in four areas. In the detection mode, four sets of data were obtained [13]. On 6 April 2021 (UTC), the CE-4 lander and Yutu-2 rover entered the 29th lunar day work period. ...
... Remote Sens. 2021,13, 2359 ...
Article
Full-text available
In-situ measurements of the spectral information on the lunar surface are of significance to study the geological evolution of the Moon. China’s Chang’E-4 (CE-4) Yutu-2 rover has conducted several in-situ spectral explorations on the Moon. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired a series of in-situ spectra of the regolith at the landing site. In general, the mineralogical research of the lunar surface relies on the accuracy of the in-situ data. However, the spectral measurements of the Yutu-2 rover may be affected by shadows and stray illumination. In this study, we analyzed 106 CE-4 VNIS spectra acquired in the first 24 lunar days of the mission and noted that six of these spectra were affected by the shadows of the rover. Therefore, a method was established to correct the effects of the rover shadow on the spectral measurements. After shadow correction, the FeO content in the affected area is corrected to 14.46 wt.%, which was similar to the result calculated in the normal regolith. Furthermore, according to the visible images, certain areas of the explored sites were noted to be unusually bright. Considering the reflectance, geometric information, and shining patterns of the multi-layer insulation (MLI), we examined the influence of the specular reflection of the MLI on the bright spot regionsd , and found that the five sets of data were likely not affected by the specular reflection of the MLI. The results indicated that the complex illumination considerably influences the in situ spectral data. This study can provide a basis to analyze the VNIS scientific data and help enhance the accuracy of interpretation of the composition at CE-4 landing sites.
... The next generation MicrOmega instruments are in flight onboard Hayabusa-2 JAXA mission [32], and in preparation for ExoMars 2020 rover [48]. Chinese lunar rover Yutu (operated in 2013), a part of the Chang'e-3 mission, was equipped with the VIS-range AOTF camera and an IR pencil-beam spectrometer [31]. This is so far the only AOTF hyper-spectral imager operated in space. ...
... It was designed by Shanghai Institute of Technical Physics, Chinese Academy of Sciences. VNIS consisted of an optical block and an electronics unit [31,67,68]. The optical block installed in front of the Yutu rover at the height of 69 cm from the surface included two spectral channels, both using AOTFs. ...
Article
Full-text available
Spectrometers employing acousto-optic tunable filters (AOTFs) rapidly gain popularity in space, and in particular on interplanetary missions. They allow for reducing volume, mass, and complexity of the instrumentation. To date, space operations of 11 AOTF spectrometers are reported in the literature. They were used for analyzing ocean color, greenhouse gases, atmospheres of Mars and Venus, and for lunar mineralogy. More instruments for the Moon, Mars, and asteroid mineralogy are in flight, awaiting launch, or in the state of advanced development. The AOTFs are used in point (pencil-beam) spectrometers for selecting echelle diffraction orders, or in hyperspectral imagers and microscopes. We review the AOTF-employing devices flown in space or ready to set off. The paper considers basic principles of the AOTF and science applications of the AOTF spectrometers, and describes developed instruments in some detail. We also address some advanced developments for future missions and plans. In addition, we discuss lessons learned during instrument design, build, calibration, and exploitation, and advantages and limitations in implementing the AOTF-based systems in space instrumentation.
... It is also a part of the analytical laboratory of the ExoMars 2020 rover mission [32]. AOTF spectrometers for surface characterization were developed in China; one of them successfully flown on Chang'e-3 lunar mission [33,34]. Similar pencil-beam AOTF spectrometers are being developed for Russian lunar landers, and to be installed at the ExoMars 2020 rover mast [35]. ...
... One obvious application is observation of a static or slow moving scene, e.g., from a synchronized orbit, planetary lander or rover. Indeed the only imaging AOTF flown to date is the visible channel of the Chinese VNIS instrument operated on Yutu rover [34]. In this case the frame imaging becomes an advantage (no scanning needed), and the depleted sensitivity could be compensated by longer exposure time. ...
... The Yutu lunar rover in the Chang'e-3 mission carried the VNIS, which was the first AOTF hyperspectral imager to realize in situ measurement in deep space [16,[26][27][28][29]. The main objectives of the mission are to perform visible and near-infrared spectral imaging (400-900 nm) and short-wave infrared spectral measurements (900-2400 nm) of the lunar surface targets. ...
Article
Full-text available
Spectrometers based on acousto-optic tunable filters (AOTFs) have several advantages, such as stable temperature adaptability, no moving parts, and wavelength selection through electrical modulation, compared with the traditional grating and Fourier transform spectrometers. Therefore, AOTF spectrometers can realize stable in situ measurement on the lunar surface under wide temperature ranges and low light environments. AOTF imaging spectrometers were first employed for in situ measurement of the lunar surface in the Chinese Chang’e project. The visible and near-infrared imaging spectrometer and the lunar mineralogical spectrometer have been successfully deployed on board the Chang’e-3/4 and Chang’e-5 missions. In this review, we investigate the performance indicators, structural design, selected AOTF performance parameters, data acquisition of the three lunar in situ spectral instruments used in the Chang’e missions. In addition, we also show the scientific achievement of lunar technology based on in situ spectral data.
... The locations of the VNIS measurements are shown in Figure 1. The VNIS raw data are reduced into level 2B radiance through a series of processing pipelines including dark-current, scattering-background subtractions, flat-field, instrument temperature corrections, and radiometric and geometric calibrations [23,24], and then distributed by the Ground Research and Application System (GRAS) of Chinese Lunar Exploration Program. The level 2B VNIS radiance data are further processed to extract diagnostic absorption characteristics and identify the surface mineralogy of exploration sites in this study. ...
Article
Full-text available
The exploration of mafic anomaly in South Pole-Aitken (SPA, the largest confirmed) basin on the Moon provides important insights into lunar interior. The landing of Chang’e-4 (CE-4) and deployment of Yutu-2 rover on the discontinuous ejecta from Finsen crater enabled in-situ measurements of the unusual mineralogy in the central portion of SPA basin with visible and near-infrared imaging spectrometer (VNIS). Here we present detailed processing procedures based on the level 2B data of CE-4 VNIS and preliminary mineralogical results at the exploration area of Yutu-2 rover. A systematic processing pipeline is developed to derive credible reflectance spectra, based on which several spectral and mineral indices are calculated to constrain the mafic mineralogy. The mafic components in the soils and boulder around CE-4 landing site are concluded as clinopyroxene-bearing with intermediate composition and probably dominated by pigeonite although the possibility of mixing orthopyroxen (OPX) and calcic clinopyroxene (CPX) also exists. These mineralogical results are more consistent with a petrogenesis that the CE-4 regolith and rock fragment are derived from rapid-cooling magmatic systems and we interpret that the materials at the CE-4 landing site ejected from Finsen crater are probably recrystallized from impact melt settings.
... The VNIS is used to detect lunar surface objects, and the optical axis of the VIS/NIR and SWIR channels is paralleled each other at an 18 mm distance. [12][13][14] The FOVs in the VIS/NIR and SWIR are 8.5 ○ × 8.5 ○ and Φ3.58 ○ , respectively. The geometrical characteristics of imaging in the VIS/NIR band and spectral detection in the SWIR, obtained by testing and calibration on the ground, are shown in Fig. 9. ...
Article
Full-text available
Chang’e 4 is a robotic lunar exploration mission operated by the China National Space Administration and was to pull off the first-ever soft landing of space hardware on the mysterious lunar far side. The Visible and Near-IR Imaging Spectrometer (VNIS) is one of the main scientific instruments onboard the Chang’e 4 lunar rover. In order to analyze the lunar surface mineral composition, the VNIS was mounted on the front of the rover and detects lunar objects with a 45° visual angle to obtain spectra and geometry data to make mineralogical and compositional measurements. The VNIS is the same as the one in the Chang’e 3 Yutu rover and consists of a visible and near-infrared imaging spectrometer (0.45–0.95 µm), a shortwave IR spectrometer (0.9–2.4 µm), and a calibration unit with dust-proofing functionality. Here, we describe detection and calibration characteristics of the VNIS, which provides valuable information for scientific data processing and applications.
Article
Full-text available
The Chang’e-4 (CE-4) lunar rover, equipped with a visible and near-IR imaging spectrometer (VNIS) based on acousto-optic tunable filter spectroscopy, was launched to the far side of the moon on December 8, 2018. The detection band of the VNIS ranges from 0.45 to 2.4 μm. Because of the weak reflection of infrared radiation from the lunar surface, a static electronic phase-locked acquisition method is adopted in the infrared channel for signal amplification. In this paper, full-link simulations and modeling are conducted on the infrared channel information flow of the instrument. The signal characteristics of the VNIS are analyzed in depth, and the signal to noise ratio (SNR) prediction and laboratory verification are presented. On 4 January 2019, the VNIS started working successfully and acquired high-resolution spectrum data of the far side of the moon for the first time. Through analysis we have found that the SNR ratio is in line with our predictions, and the data obtained by VNIS in orbit are consistent with the information model proposed in this paper.
Article
Full-text available
The Visible and Near-Infrared Imaging Spectrometer (VNIS), using two acousto-optic tunable filters as dispersive components, consists of a VIS/NIR imaging spectrometer (0.45─0.95 μm), a shortwave IR spectrometer (0.9─2.4 μm) and a calibration unit with dust-proofing functionality. The VNIS was utilized to detect the spectrum of the lunar surface and achieve in-orbit calibration, which satisfied the requirements for scientific detection. Mounted at the front of the Yutu rover, lunar objects that are detected with the VNIS with a 45° visual angle to obtain spectra and geometrical data in order to analyze the mineral composition of the lunar surface. After landing successfully on the Moon, the VNIS performed several explorations and calibrations, and obtained several spectral images and spectral reflectance curves of the lunar soil in the region of Mare Imbrium. This paper describes the working principle and detection characteristics of the VNIS and provides a reference for data processing and scientific applications.
Conference Paper
Full-text available
The Acousto-Optical Tunable Filter (AOTF) is an electronically tunable optical filter based on Acousto-optic effect and has its own special compared with other dispersive parts. Because its characteristics of electronic tunable spectral selection, rapid response and simple structure, imaging spectrometer based on AOTF is a useful high-spectral technology, especially in deep space exploration applications. This paper introduces two imaging spectrometers, a VIS-NIR Imaging Spectrometer (VNIS) built as a payload instrument for lunar detection and a whiskbroom imaging spectrometer (WIS) with programmable spectral sampling. VNIS provides programmable spectral selection from 0.45 to 2.4 μm and includes two channels, a V-NIR hyper-spectral imager (0.45 to 0.95μm) and a SWIR spectrograph (0.9 to 2.4μm), with a spectral overlap of 0.05μm. WIS is a kind of scanning, spectral programmable imaging spectrometer, includes a scanning mechanism and a programmable spectral selection spectrometer. In the end, the prospects in deep-space exploration application are discussed.
Article
Full-text available
In order to conduct lunar surface mineral composition studies and content analysis, the Visible and Near-infrared Imaging Spectrometer (VNIS), one of the scientific payloads of the Chang’E 3 Yutu rover, has been developed to detect lunar surface objects and to obtain their reflectance spectra and geometric images. This is achieved with a 45° visual angle and at a height of 0.69 m. VNIS is equipped with a lunar surface calibration function, and the spectral range is 0.45–2.40 μm with a spectral resolution of 2–12 nm. It is capable of synchronously acquiring the full spectrum of lunar surface objects and in situ calibration. Here, we describe the VNIS and explain the preliminary results of the lunar surface exploration and calibration, which provides valuable information for scientific data processing and applications.
Article
Full-text available
The Acousto-Optic Tunable Filter (AOTF) is an electronically tunable optical filter based on Acousto-optic effect and has its own special compared with other dispersive parts. Imaging spectrometer based on acousto-optic tunable filter (AOTF) is a useful high-spectral technology, especially in deep space exploration applications because its characteristics of staring imaging, electronic tunable spectral selection and simple structure. Because the diffraction of light in AOTF filters is dependent on both wavelength and angle of incidence, the Spectral and geometrical calibration must therefore be performed over the entire spectral range of AOTF hyper-spectral imaging systems. In this paper, the dispersive principle of AOTF is introduced firstly and its application predominance in space-based spectral detection is analyzed. Then, a method for calibration of acousto-optic tunable filter (AOTF) hyper-spectral imaging systems is proposed and evaluated. This paper introduces the calibration of a VIS-NIR Imaging Spectrometer (VNIS) by the method. The VNIS is a payload instrument for lunar detection and provides programmable spectral selection from 0.45 to 0.95μm. The results indicate that the method is accurate and efficient. Therefore, the proposed method is suitable for spectral and geometrical calibration of imaging spectrometers based on AOTF.
Article
Full-text available
The second phase of the Chang'E Program (also named Chang'E-3) has the goal to land and perform in-situ detection on the lunar surface. A VIS/NIR imaging spectrometer (VNIS) will be carried on the Chang'E-3 lunar rover to detect the distribution of lunar minerals and resources. VNIS is the first mission in history to perform in-situ spectral measurement on the surface of the Moon, the reflectance data of which are fundamental for interpretation of lunar composition, whose quality would greatly affect the accuracy of lunar element and mineral determination. Until now, in-situ detection by imaging spectrometers was only performed by rovers on Mars. We firstly review reflectance conversion methods for rovers on Mars (Viking landers, Pathfinder and Mars Exploration rovers, etc). Secondly, we discuss whether these conversion methods used on Mars can be applied to lunar in-situ detection. We also applied data from a laboratory bidirectional reflectance distribution function (BRDF) using simulated lunar soil to test the availability of this method. Finally, we modify reflectance conversion methods used on Mars by considering differences between environments on the Moon and Mars and apply the methods to experimental data obtained from the ground validation of VNIS. These results were obtained by comparing reflectance data from the VNIS measured in the laboratory with those from a standard spectrometer obtained at the same time and under the same observing conditions. The shape and amplitude of the spectrum fits well, and the spectral uncertainty parameters for most samples are within 8%, except for the ilmenite sample which has a low albedo. In conclusion, our reflectance conversion method is suitable for lunar in-situ detection.
Article
To analyze the composition of lunar surface minerals, one of the scientific payloads of the Chang™E 3 Yutu rover, the Visible and Near-infrared Imaging Spectrometer (VNIS), was developed to detect lunar surface objects and to obtain their reflectance spectra and geometric images. The VNIS, which uses acousto-optic tunable filters as dispersive components, consists of a VIS/NIR imaging spectrometer (0.45-0.95 μm), a shortwave IR spectrometer (0.9-2.4 μm), and a calibration unit with dust-proofing functionality. It is capable of synchronously acquiring the full spectra of lunar surface objects and performing in-situ calibration. After landing successfully on the Moon, the VNIS performed several explorations and calibrations, and obtained several spectral images and spectral reflectance curves of the lunar soil in the Imbrium region. This paper introduces the VNIS, including its working principle, implementation, operation, and major specifications, as well as the initial scientific achievement of lunar surface exploration.
Article
The Chang'e-3 Visible and Near-infrared Imaging Spectrometer (VNIS) is one of the four payloads on the Yutu rover. After traversing the landing site during the first two lunar days, four different areas are detected, and Level 2A and 2B radiance data have been released to the scientific community. The released data have been processed by dark current subtraction, correction for the effect of temperature, radiometric calibration and geometric calibration. We emphasize approaches for reflectance analysis and mineral identification for in-situ analysis with VNIS. Then the preliminary spectral and mineralogical results from the landing site are derived. After comparing spectral data from VNIS with data collected by the M3 instrument and samples of mare that were returned from the Apollo program, all the reflectance data have been found to have similar absorption features near 1000 nm except lunar sample 71061. In addition, there is also a weak absorption feature between 1750~2400 nm on VNIS, but the slopes of VNIS and M3 reflectance at longer wavelengths are lower than data taken from samples of lunar mare. Spectral parameters such as Band Centers and Integrated Band Depth Ratios are used to analyze mineralogical features. The results show that detection points E and N205 are mixtures of high-Ca pyroxene and olivine, and the composition of olivineat point N205 is higher than that at point E, but the compositions of detection points S3 and N203 are mainly olivine-rich. Since there are no obvious absorption features near 1250 nm, plagioclase is not directly identified at the landing site.
Article
Sensing from space requires the development of hyperspectral imagers operating in the two atmospheric window regions (3-5 mum and 8-12 mum) in the infrared region. At the Army Research Laboratory we are developing hyperspectral imagers operating in these two regions based on using acousto-optic tunable filters (AOTFs). Research is going on in the growth of new acousto-optic materials-mercurous halides (Hg2Cl2 and Hg2Br2) and tellurium (Te) for development of AOTF cells. We have developed a hyperspectral imager using a tellurium dioxide (TeO2) AOTF with a liquid-nitrogen-cooled indium antimonide (InSb) 256×256 focal plane array (FPA) that covers 2-4.5 mum region and another imager using a thallium arsenic selenide (TAS) AOTF with liquid-nitrogen-cooled mercury cadmium telluride (HgCdTe) 256×256 FPA to cover 7.8-9.8 mum region. Each of these imagers has been integrated on a tripod-mountable platform with an appropriate optical train. Control of RF electronics, and image acquisition and storage operations are carried out under full computer-control with a user-friendly interface. We will discuss the progress in material development and present imaging results.