Lunar Observations Research Articles

Limit on the ultrahigh-energy neutrino flux from lunar observations with the Parkes radio telescope

We report a limit on the ultra-high-energy neutrino flux based on a non-detection of radio pulses from neutrino-initiated particle cascades in the Moon, in observations with the Parkes radio telescope undertaken as part of the LUNASKA project. Due to the improved sensitivity of these observations, which had an effective duration of 127 hours and a frequency range of 1.2-1.5 GHz, this limit extends to lower neutrino energies than those from previous lunar radio experiments, with a detection threshold below 10^20 eV. The calculation of our limit allows for the possibility of lunar-origin pulses being misidentified as local radio interference, and includes the effect of small-scale lunar surface roughness. The targeting strategy of the observations also allows us to place a directional limit on the neutrino flux from the nearby radio galaxy Centaurus A.

On-orbit calibration of the Suomi National Polar-Orbiting Partnership Visible Infrared Imaging Radiometer Suite for ocean color applications.

The NASA Ocean Biology Processing Group (OBPG) developed two independent calibrations of the Suomi National Polar-Orbiting Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) moderate resolution reflective solar bands using solar diffuser measurements and lunar observations, and implemented a combined solar- and lunar-based calibration to track temporal changes in radiometric response of the instrument. Differences between the solar and lunar data sets have been used to identify issues and verify improvements in each. Linearization of the counts-to-radiance conversion yields a more consistent calibration at low radiance levels. Correction of a recently identified error in the VIIRS solar unit vector coordinate frame has been incorporated into the solar data and diffuser screen transmission functions. Temporal trends in the solar diffuser stability monitor data have been evaluated and addressed. Fits to the solar calibration time series show mean residuals per band of 0.067%-0.17%. Periodic residuals in the VIIRS lunar data are confirmed to arise from a wavelength-dependent libration effect for the sub-spacecraft point in the output of the U.S. Geological Survey Robotic Lunar Observatory photometric model of the Moon. Temporal variations in the relative spectral responses for each band have been assessed, and significant impact on band M1 (412 nm) lunar data has been identified and rectified. Fits to the lunar calibration time series, incorporating sub-spacecraft point libration corrections, show mean residuals per band of 0.069%-0.20%. Lunar calibrations have been used to adjust the solar-derived radiometric corrections for bands M1, M3, and M4. After all corrections, the relative differences in the solar and lunar calibrations for bands M1-M7 are 0.093%-0.22%. The OBPG has achieved a radiometric stability for the VIIRS on-orbit calibration that is commensurate with those achieved for SeaWiFS and Aqua MODIS, supporting the incorporation of VIIRS data into the long-term NASA ocean color data record.

Atom & cosmos: Europa's geysers play hard‐to‐see: Further observations of Jovian moon fail to detect venting

Science NewsVolume 187, Issue 2 p. 7-7 News Atom & cosmos: Europa's geysers play hard-to-see: Further observations of Jovian moon fail to detect venting Andrew Grant, Andrew GrantSearch for more papers by this author Andrew Grant, Andrew GrantSearch for more papers by this author First published: 12 January 2015 https://doi.org/10.1002/scin.2015.187002004Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume187, Issue224 January 2015Pages 7-7 RelatedInformation

Monitoring of COMS MI visible channel degradation based on Moon observations

Most of the current space-borne visible imagers on a geosynchronous orbit (GEO), which do not have onboard calibration devices, use a vicarious calibration. For a meteorological payload on a GEO satellite, lunar calibration is often used. The meteorological imager (MI) on the communication, ocean, and meteorological satellite (COMS) has been successfully operated for half of its entire mission lifetime (∼7 years). The visible channel of the MI uses the lunar calibration to monitor its degradation. The degradation rate of the instrument was monitored using the ratio between the calculated radiance of the Moon from the Robotic Lunar Observatory (ROLO) model and the observed radiance from the MI. Analyses of the 42-month Moon image data showed that the instrument’s mean degradation rate was about 1.88%. These values confirmed the outstanding performance of the COMS MI visible channel compared with that of the GOES-10 imager.

End-to-end simulation model of rover-based hyperspectral remote-sensing systems: application to VNIS

The simulation of remote-sensing hyperspectral images has various applications such as the design of future hyperspectral imaging systems, understanding of the image formation process, development and validation of data processing algorithms, and optimization of the instrument imaging mode. For incomplete understanding of the lunar surface and the wide environmental differences between earth and moon observation, imaging systems for lunar observation cannot be tested in their exact working environments before launch. In these cases, simulation of lunar hyperspectral images can be used as a powerful tool to analyse the imaging process on the moon. The VIS–NIR imaging spectrometer (VNIS) aboard the Chang’e-3 (CE-3) lunar rover is used to perform in situ mineral detection on the lunar surface, but the rover-based VNIS has some additional effects from the rover itself (e.g. the shadow caused by the rover). In this paper, a rover-based radiative transfer model has been developed, and the simulation model is able to generate realistic VNIS-like data in an automatic way under a set of user-driven instrument and illumination parameters. A realistic surface reflectance cube, as the original input for the simulation model, is provided by the interference imaging spectrometer (IIM) data of Chang’e-1 (CE-1). Several hyperspectral simulations in different illumination and observation geometries have been conducted to analyse the effects of shadow, specular irradiance, and diffuse irradiance on the imaging data. For certain illumination geometries, the simulation model can forecast image quality in different observation geometries; the model can also determine the optimal observation azimuth ranges at different solar elevation angles. Moreover, the simulation model can be used to provide test images for the rover effect elimination algorithms. These applications of the model can facilitate understanding by analysing the rover-based hyperspectral remote-sensing process and eventually obtaining high-quality images of the lunar surface.

Evaluation of Radiometric Improvements With Electronic Crosstalk Correction for Terra MODIS Band 27

The MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands, covering a wavelength range from 0.4 to 14.4 μm. Terra MODIS band 27 (6.72 μm), a water vapor band, was found to have electronic crosstalk from other bands located on the same focal plane assembly, which causes surface feature contamination and pronounced detector level striping in the images. In a previous study, an algorithm using a linear approximation derived from on-orbit lunar observations was developed to correct the crosstalk effect. Results demonstrated that the correction substantially reduces the striping and removes the contaminated surface features. However, it was also demonstrated that the crosstalk effect might bring about a long-term increase in the brightness temperatures (BTs) in Terra band 27. In this paper, it is shown that there is a long-term drift (or decrease), which is strongly detector dependent, in the BT for the band induced by the crosstalk effect. It is also shown that the crosstalk correction with the linear algorithm substantially removes the detector-dependent long-term drift and greatly improves the radiometric accuracy of the band. The comparison between the BT of Terra band 27 in the most recent MODIS Level 1B (L1B) collection [Collection 6 (C6)] and those from the Infrared Atmospheric Sounding Interferometer using simultaneous-nadir-overpass observations shows that the detector-averaged long-term drift in the BT in Terra band 27 varies from approximately 1 K to 3 K. The detector difference can be as large as 9 K for a few detectors during the last five years in the northern and southern polar areas. With crosstalk correction applied, the long-term drift is reduced to be less than 0.5 K, and the detector difference is within 1 K. The crosstalk effect-induced detector-dependent long-term drift in Terra band 27 and the capability of the crosstalk correction algorithm to remove the drift are also assessed at three well-characterized sites with different radiance levels, namely, Dome Concordia (Dome C), Libya 1, and the Pacific Ocean at various radiometric levels. The long-term drift and the strong detector dependence of the drift are clearly observed at the three sites with the BT in the Terra band 27 C6 L1B products. The band-averaged BT drifts are about 0.8 K, 5 K, and 5.5 K, and the detector differences can be as large as 4 K, 12 K, and 15 K, respectively, for the three sites. With the crosstalk correction applied, the long-term drifts in the BT over the three sites are substantially removed, and the observed detector differences of Terra band 27 at the three sites are also significantly reduced. The crosstalk correction greatly improves the radiometric accuracy of the band as well as the image quality.

On-Orbit Characterization of MODIS Modulation Transfer Function Using the Moon

The high-contrast edge of the Moon has been used for the on-orbit measurement of the modulation transfer function (MTF) of remote sensing instruments with a lunar observation capability. With the lunar edge as a target, the classical edge method is applied to the National Aeronautics and Space Administration's MODerate resolution Imaging Spectroradiometer (MODIS) on board the Terra and Aqua satellites. One of the major difficulties encountered during the calculation is that the spatial resolution of MODIS is too coarse to capture the fine structure of the edge spread function (ESF), which is required to calculate the MTF. To produce the MODIS ESF in high resolution, lunar images of a selected edge acquired by multiple instrument scans need to be superposed by aligning the edge positions accurately. In this paper, an algorithm is developed to perform the alignment, based on the lunar position data generated by the MODIS geolocation algorithm and recorded scan by scan. The positions of the lunar edges at the focal plane are calculated scan by scan, allowing the construction of a high-quality ESF for MTF derivation. The algorithm is applied to all MODIS bands with 250-m, 500-m, and 1-km spatial resolutions in both along-scan and along-track directions. The along-track MTF results are particularly valuable because the onboard SpectroRadiometric Calibration Assembly can only monitor the along-scan MTF. The trending results show that the along-track MTF of MODIS has been stable throughout the MODIS lifetime and is well above the design specification for all bands. The limitation of the algorithm is analyzed. The algorithm developed in this paper can be applied to other instruments with similar design features.

Time-Dependent Response Versus Scan Angle for MODIS Reflective Solar Bands

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments currently operate onboard the National Aeronautics and Space Administration (NASA's) Terra and Aqua spacecraft, launched on December 18, 1999 and May 4, 2002, respectively. MODIS has 36 spectral bands, among which 20 are reflective solar bands (RSBs) covering a spectral range from 0.412 to 2.13 μm. The RSBs are calibrated on orbit using a solar diffuser (SD) and an SD stability monitor and with additional measurements from lunar observations via a space view (SV) port. Selected pseudo-invariant desert sites are also used to track the RSB on-orbit gain change, particularly for short-wavelength bands. MODIS views the Earth surface, SV, and the onboard calibrators using a two-sided scan mirror. The response versus scan angle (RVS) of the scan mirror was characterized prior to launch, and its changes are tracked using observations made at different angles of incidence from onboard SD, lunar, and Earth view (EV) measurements. These observations show that the optical properties of the scan mirror have experienced large wavelength-dependent degradation in both the visible and near infrared spectral regions. Algorithms have been developed to track the on-orbit RVS change using the calibrators and the selected desert sites. These algorithms have been applied to both Terra and Aqua MODIS Level 1B (L1B) to improve the EV data accuracy since L1B Collection 4, refined in Collection 5, and further improved in the latest Collection 6 (C6). In C6, two approaches have been used to derive the time-dependent RVS for MODIS RSB. The first approach relies on data collected from sensor onboard calibrators and mirror side ratios from EV observations. The second approach uses onboard calibrators and EV response trending from selected desert sites. This approach is mainly used for the bands with much larger changes in their time-dependent RVS, such as the Terra MODIS bands 1-4, 8, and 9 and the Aqua MODIS bands 8 and 9. In this paper, the algorithms of these approaches are described, their performance is demonstrated, and their impact on L1B products is discussed. In general, the shorter wavelength bands have experienced a larger on-orbit RVS change, which, in general, are mirror side and detector dependent. The on-orbit RVS change due to the degradation of band 8 can be as large as 35% for Terra MODIS and 20% for Aqua MODIS. Vital to maintaining the accuracy of the MODIS L1B products is an accurate characterization of the on-orbit RVS change. The derived time-independent RVS, implemented in C6, makes an important improvement to the quality of the MODIS L1B products.

VIIRS On-Orbit Spatial Characterization Using the Moon

The VIIRS instrument onboard the Suomi-NPP satellite was launched in October 2011. The design and operation of its on-orbit calibration system are strongly based on MODIS heritage. However, VIIRS has no onboard calibrator similar to the spectro-radiometric calibration assembly (SRCA) on MODIS to perform the sensor on-orbit spatial characterization of band-to-band registration (BBR) and modulation transfer function (MTF). The Moon has been known as a spectrally, radiometrically, and geometrically stable source that can be used for sensor on-orbit calibration and characterization. In this letter, the algorithms developed and validated for MODIS spatial characterization using the Moon are briefly summarized and extended to VIIRS. The BBR in both along-scan and along-track directions and the MTF in the along-track direction are calculated with the scheduled VIIRS lunar observations and presented. These early results confirm that the VIIRS spatial characterization parameters have been stable since launch and are within the performance specification. The along-scan MTF cannot be accurately determined using the same algorithm and is not included in this study because the movement of the Moon in this direction is too limited to construct an edge spread function for MTF derivation. As part of the VIIRS on-orbit calibration and validation effort, the BBR and MTF parameters will be continuously monitored and evaluated throughout its mission lifetime.

VIIRS on‐orbit calibration methodology and performance

AbstractThe Visible Infrared Imaging Radiometer Suite (VIIRS) sensor aboard the Suomi National Polar‐orbiting Partnership spacecraft has successfully operated since its launch in October 2011. The VIIRS collects data in 22 spectral bands that are calibrated by a set of onboard calibrators (OBC). In addition, lunar observations are made to independently track VIIRS long‐term calibration stability for the reflective solar bands (RSB). This paper provides an overview of VIIRS OBC functions as well as its on‐orbit operation and calibration activities. It also describes sensor calibration methodologies and demonstrates VIIRS on‐orbit performance from launch to present. Results reported in this paper include on‐orbit changes in sensor spectral band responses, detector noise characterization, and key calibration parameters. Issues identified and their potential impacts on sensor calibration are also discussed. Since launch, the VIIRS instrument nominal operation temperature has been stable to within ±1.0 K. The cold focal plane temperatures have been well controlled, with variations of less than 20 mK over a period of 1.5 years. In general, changes in thermal emissive bands (TEB) detector responses have been less than 0.5%. Despite large response degradation in several near‐infrared and short‐wave infrared bands and large SD degradation at short visible wavelengths, the VIIRS sensor and OBC overall performance has been excellent postlaunch. The degradation caused by the telescope mirror coating contamination has been modeled and its impact addressed through the use of modulated relative spectral response in the improved calibration and the current sensor data record data production. Based on current instrument characteristics and performance, it is expected that the VIIRS calibration will continue to meet its design requirements, including RSB detector signal to noise ratio and TEB detector noise equivalent temperature difference, throughout its 7 year design lifetime.

Point response function of the Clouds and Earth Radiant Energy System scanning radiometer

An overview of work related to the point response function (PRF) of the Clouds and Earth Radiant Energy System (CERES) scanning radiometer is presented. The aspects of the CERES design that affect the PRF are described, and then the design of the PRF is explained. The PRF was designed by shaping the field of view so as to minimize the blur plus alias errors of the radiance field reconstructed from the CERES measurements. The design is conducted in the Fourier domain. The PRF can then be computed by transforming the resulting transfer function to the physical domain. Alternatively, the PRF can be computed in the physical plane. The PRF of each model of the CERES instrument has been tested in the Radiation Calibration Facility by use of a PRF source and compared well with prediction. CERES instruments are aboard the Terra, Aqua, and Suomi-NPP spacecraft. In orbit, lunar observations are used to validate the PRF. These results showed nominal performance except for the longwave window channel of flight model 2, for which a region of anomalously high sensitivity was found.

Terra MODIS Band 27 Electronic Crosstalk Effect and Its Removal

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the National Aeronautics and Space Administration Earth observing system. The first MODIS instrument was launched in December, 1999 onboard the Terra spacecraft. MODIS has 36 bands, covering a wavelength range 0.4-14.4 μm. MODIS band 27 (6.72 μm) is a water vapor band, which is designed to be insensitive to Earth surface features. In recent Earth view images of Terra band 27, surface feature contamination is clearly seen with pronounced striping. In this paper, it is shown that these band-27 issues are caused by electronic crosstalk from bands 28-30. An algorithm using a linear approximation is developed to correct the crosstalk effect. The crosstalk coefficients are derived from Terra MODIS lunar observations. They show that the crosstalk is strongly detector-dependent and the crosstalk pattern has changed in a noticeable fashion since launch. The crosstalk contributions were positive to the instrument response of band 27 early in the mission but became negative and much larger in magnitude at later stages of the mission for most detectors of the band. The algorithms are applied to both the black body (BB) calibration and the MODIS L1B calibrated products. With the crosstalk effect significantly removed, the calibration coefficients of Terra MODIS band 27 derived from the BB show that the detector differences become smaller. With the algorithms applied to MODIS L1B products, the Earth surface features are significantly removed, thereby restoring the radiometric balance of the band and substantially reducing the striping features in the image.

Compensating for the Effects of Stray Light in Single-Monochromator Brewer Spectrophotometer Ozone Retrieval

Spectrometers are designed to isolate particular wavebands and suppress light from wavelengths outside the band of interest. However, a small amount of undesired light will always enter the detector, not through the designed optical path, but through random scattering from the instrument optical components, housing, and dust particles. Every spectrophotometer has stray light coming from outside the nominal measurement waveband. For Dobson spectrophotometers and single monochromator Brewer spectrophotometers, which are basic instruments in the World Meteorological Organization (WMO) ozone and ultraviolet (UV) monitoring network, the error introduced by stray light is substantial when the ozone slant path becomes very large because of high solar zenith angles and a thick ozone layer. These are common conditions during Arctic spring. To study the issue, a long ozone slant path Intercomparison/Calibration campaign for Nordic Brewers and Dobsons was held at Sodankylä 8–24 March 2011 and a follow-up campaign to extend calibrations to shorter ozone slant paths took place at Izaña observatory, Tenerife, between 28 October and 18 November 2011. These campaigns were part of the Committee on Earth Observation Satellites (CEOS) Intercalibration of Ground-based Spectrometers and Lidars project funded by the European Space Agency (ESA), intended to permit the homogenization of ozone data from the European ozone ground-truthing network. During the active intercomparison periods, measurements were taken only when good conditions for sun or moon observations existed. Laboratory measurements using calibration lamps and helium-cadmium (HeCd) lasers were an essential part of both campaigns. The campaigns produced a high-quality database of total ozone and UV measurements and an accurate, up-to-date calibration and characterization of participating Brewers and Dobsons against the European standard instruments from the Regional Dobson Calibration Centre-Europe (RDCC-E) and the Regional Brewer Calibration Centre-Europe (RBCC-E). In the present work we focus on single monochromator Brewers and present a physics-based method to compensate for the stray-light effects in ozone retrieval using laboratory characterizations and radiative transfer modelling. The method was tested with independent data from the campaign.

Lunar Observation Support System Using Smartphone AR for Astronomy Education

It is possible to improve learnersâ?? understanding of the concept of lunar phases by using Observation based Learning (OBL). In this research, Smartphone Augmented Reality (AR) technology was used to develop a multi-viewpoint AR-based mobile learning (M-VARML) system for moon observation that can be used in the real world environment. An experiment was conducted to evaluate the usefulness of our system. Participants were given five moon observation tasks, which they had to perform manually and using the M-VARML system. After each task, they were given follow-up questionnaires on the usefulness of the functions in the system. Finally, they were asked about the operational usability and the effect our system had in motivating them to pursue lunar observation. The results show that the M-VARML system is effective in improving the observation and learning of students and in enhancing their motivation to pursue lunar learning.

On the chronology of lunar origin and evolution

An origin of the Moon by a Giant Impact is presently the most widely accepted theory of lunar origin. It is consistent with the major lunar observations: its exceptionally large size relative to the host planet, the high angular momentum of the Earth–Moon system, the extreme depletion of volatile elements, and the delayed accretion, quickly followed by the formation of a global crust and mantle.

월면 디지털 영상 분석을 이용한 대기 광학두께 산출

이 연구에서는 상용 디지털 카메라를 이용하여 야간에 촬영된 월면 영상을 분석하여 야간의 대기 광학두께와 에어로솔 광학두께를 추정하였다. 기본적으로 랑리회귀법을 이용하였으며 구름이 없고 대기의 광학적 특성이 비교적 안정한 날에 관측을 수행하였다. 카메라의 적색(R), 녹색(G), 청색(B) 채널의 파장별 반응함수를 이용하여 월광관측에 대한 유효 중심파장 및 레일리 광학두께를 추정하였으며, 랑리 회귀법에서 유도된 대기광학두께로부터 레일리 광학두께를 제하여 에어로솔 광학 두께를 산출하였다. 야간에는 독립적인 방법으로 산출된 검증자료나 다른 에어로솔 광학두께 자료가 거의 없으므로 월면 관측이 이루어지기 수 시간 전의 주간에 정밀한 태양분광광도계로 측정된 에어로솔 광학두께 자료와 MODIS 위성센서 관측으로부터 산출된 에어로솔 광학두께 자료를 본 연구에서 월면 관측을 통해 산출된 자료와 비교하였다. 비교 결과 R, G, B 채널에서 대략 0.1정도의 오차 범위에서 월면 영상분석을 통해 에어로솔 광학두께의 추정이 가능함을 알 수 있었다. 단, 대기 중의 에어로솔 입자들의 크기를 나타내는 모수인 앙스트롬지수(<TEX>${\AA}$</TEX>ngstr<TEX>$\ddot{o}$</TEX>m Exponent)는 파장별 광학두께의 작은 오차에도 큰 오차를 가질 수 있기 때문에 에어로솔 광학두께의 오차에 비해 비교적 큰 오차를 보일 수 있음이 나타났다. 그럼에도 불구하고, 야간의 에어로솔 광학두께 자료가 많지 않은 현실에서 저비용으로 월면 관측을 통하여 에어로솔 광학두께를 산출할 수 있는 가능성을 찾았다는 점에서 본 연구의 의의가 있으며 앞으로 보다 많은 관측과 분석을 통해 보다 향상된 야간 에어로솔 광학두께 추정이 가능할 것으로 보인다. Atmospheric optical thickness during nighttime was estimated in this study using analysis on the images of the moon taken from commercial digital camera. Basically the Langely Regression method was applied to the observations of the moon for the cloudless and optically stable sky conditions. The spectral response functions for the red(R), green(G), and blue(B) channels were employed to derive effective wavelength centers of each channel for the observations of the moon, and the correspondent Rayleigh optical thickness were also calculated. Aerosol optical thickness (AOT) was calculated by subtracting Rayleigh optical thickness from the atmospheric optical thickness derived from the Langley regression method. As there are only handful of nighttime AOT observations, the AOT from the moon observations was compared with the AOT from sun-photometers and the MODIS satellite sensor, which was taken several hours before the moon observations of this study. As a result, the values of AOT from moon observations agree with those from sun-photometers and MODIS within 0.1 for the R, G, B channels of the digital camera. On the other hand, <TEX>${\AA}$</TEX>ngstr<TEX>$\ddot{o}$</TEX>m Exponent seems to be subject to larger errors due to its sensitiveness to the spectral errors of AOT. Nevertheless, the results of this study indicate that the method reported in this study is promising as it can provide nighttime AOT relatively easily with a low cost instrument like digital camera. More observations and analyses are warranted to attain improved nighttime AOT observations in the future.

Precise Measurement of Lunar Spectral Irradiance at Visible Wavelengths.

We report a measurement of lunar spectral irradiance with an uncertainty below 1 % from 420 nm to 1000 nm. This measurement uncertainty meets the stability requirement for many climate data records derived from satellite images, including those for vegetation, aerosols, and snow and ice albedo. It therefore opens the possibility of using the Moon as a calibration standard to bridge gaps in satellite coverage and validate atmospheric retrieval algorithms. Our measurement technique also yields detailed information about the atmosphere at the measurement site, suggesting that lunar observations are a possible solution for aerosol monitoring during the polar winter and can provide nighttime measurements to complement aerosol data collected with sun photometers. Our measurement, made with a novel apparatus, is an order of magnitude more accurate than the previous state-of-the-art and has continuous spectral coverage, removing the need to interpolate between filter passbands.

Characterization of Terra and Aqua MODIS VIS, NIR, and SWIR Spectral Bands' Calibration Stability

The Moderate Resolution Imaging Spectroradiometer (MODIS) has successfully operated onboard the Terra spacecraft for more than 12 years and the Aqua spacecraft for more than ten years. It has 20 reflective solar bands covering the visible (VIS), near infrared (NIR), and short-wave infrared (SWIR) spectral regions. They are calibrated on orbit using regularly scheduled solar diffuser measurements and lunar observations. In recent years, observations over selected ground targets are also used to monitor detector responses at different angles of incidence. This paper provides a brief description of MODIS on-orbit calibration and characterization methodologies and examines the calibration stability of the VIS, NIR, and SWIR spectral bands over the entire missions of both instruments. Results obtained from four different vicarious approaches (deserts, Dome Concordia, deep convective cloud, and simultaneous nadir overpass) show that Terra MODIS VIS and NIR spectral bands have a wavelength-dependent drift in reflectance with a drop up to 8 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\%$</tex></formula> in the shortest wavelength region. All four approaches have a relative agreement to within 2.0 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \%$</tex></formula> with an uncertainty of less than 1.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\%$</tex></formula> for most bands. It is anticipated that the improvements made in the MODIS Collection 6, with additional corrections based on the desert reflectance trending results, will significantly reduce, if not completely remove, some of the trending drifts identified in the Collection-5 data product.

Lunar opposition effect as inferred from Chandrayaan‐1 M3 data

AbstractThe shadow‐hiding and coherent backscattering enhancement mechanisms are considered to be the major contributors to the brightness opposition effect of the Moon. However, the actual proportions of the mechanisms at different phase angles still remain not well determined. In order to assess the lunar phase function across small phase angles, we utilize imaging spectrometer data acquired by the Moon Mineralogy Mapper (M3) onboard the Chandrayaan‐1 spacecraft. We calculated phase functions of apparent reflectance and color ratios in the wavelength range 541–2976 nm for several mare and highland areas. As inferred from changes in the wavelength dependence of the phase curves, the shadow‐hiding effect is a major component of the brightness opposition surge at phase angle &gt; 2°. The coherent backscattering enhancement may contribute some to the opposition effect at phase angles &lt; 2°. We found nonmonotonic behavior of color‐ratio phase curves that reveal the minimum at ~ 2–4°. Using lunar observations, this is the first reliable evidence of the colorimetric opposition effect found earlier for lunar samples.

Hyper-spectral imager of the visible band for lunar observations

A prototype hyper-spectral imager in the visible spectral band was developed for the planned Korean lunar missions in the 2020s. The instrument is based on simple refractive optics that adopted a linear variable filter and an interline charge-coupled device. This prototype imager is capable of mapping the lunar surface at wavelengths ranging from 450 to 900 nm with a spectral resolution of ∼8 nm and selectable channels ranging from 5 to 252. The anticipated spatial resolution is 17.2 m from an altitude of 100 km with a swath width of 21 km