J/AJ/155/213 Absolute reflectance & new calibration site of the Moon (Wu+, 2018) ================================================================================ The absolute reflectance and new calibration site of the Moon. Wu Y., Wang Z., Cai W., Lu Y. =2018AJ....155..213W (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Solar system ; Spectra, optical ; Spectra, infrared Keywords: instrumentation: spectrographs - planets and satellites: composition - planets and satellites: detection - techniques: imaging spectroscopy Abstract: How bright the Moon is forms a simple but fundamental and important question. Although numerous efforts have been made to answer this question such as use of sophisticated electro-optical measurements and suggestions for calibration sites, the answer is still debated. An in situ measurement with a calibration panel on the surface of the Moon is crucial for obtaining the accurate absolute reflectance and resolving the debate. China's Chang'E-3 (CE-3) "Yutu" rover accomplished this type of measurement using the Visible-Near Infrared Spectrometer (VNIS). The measurements of the VNIS, which were at large emission and phase angles, complement existing measurements for the range of photometric geometry. The in situ reflectance shows that the CE-3 landing site is very dark with an average reflectance of 3.86% in the visible bands. The results are compared with recent mission instruments: the Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC), the Spectral Profiler (SP) on board the SELENE, the Moon Mineralogy Mapper (M^3^) on board the Chandrayaan-1, and the Chang'E-1 Interference Imaging Spectrometer (IIM). The differences in the measurements of these instruments are very large and indicate inherent differences in their absolute calibration. The M^3^ and IIM measurements are smaller than LROC WAC and SP, and the VNIS measurement falls between these two pairs. When using the Moon as a radiance source for the on-orbit calibration of spacecraft instruments, one should be cautious about the data. We propose that the CE-3 landing site, a young and homogeneous surface, should serve as the new calibration site. Description: The Visible-Near Infrared Spectrometer (VNIS) uses acousto-optic tunable filters (AOTF) as dispersive components and consists of a VIS/NIR imaging spectrometer (0.45-0.95 {mu}m, 256x256 pixels, field of view: 8.5{deg}x8.5{deg}), a shortwave IR (SWIR) spectrometer (0.9-2.4 {mu}m, 1 pixel, field of view: 3.6{deg}), and a white calibration panel that is protected from dust. The default spectral sampling interval is 5 nm, and the total number of sampling bands is 400 (100 bands for the VIS imaging spectrometer and 300 bands for the SWIR spectrometer; note that the bands between 900 and 945 nm overlap). The VNIS is mounted on the front of the rover and detects lunar surface objects from a height of 0.69 m above the lunar surface at 45{deg} emission angle (Figure 2). The nominal spatial resolution of the VIS imaging spectrometer is 0.53-0.80 mm/p, and the field of view (FOV) is an isosceles trapezoid with a height of 20.6 cm and two parallel sides of 13.5 and 15.7 cm. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 66 9 Data acquisition conditions of the four sites analyzed by the Visible-Near Infrared Spectrometer (VNIS) and orbital data table2.dat 56 390 In situ radiance and Reflectance Factor (REFF) for the VNIS measurements -------------------------------------------------------------------------------- See also: J/ApJ/834/17 : Mass + radius of planets, moons, low mass stars (Chen+, 2017) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 A12 --- Site Site designation (1) 14- 23 A10 "date" Date Date of observation (UTC) 25- 29 F5.2 deg SunZ [43.54/69.57] Sun zenith angle 31- 36 F6.2 deg SunA [108.72/248.44] Sun azimuth angle 38- 46 F9.6 deg ViewZ [1.58/48.27] View zenith angle 48- 53 F6.2 deg ViewA [6/355.47] View azimuth angle 55- 60 F6.2 deg alpha [44.07/108.21] Phase angle 62- 66 F5.3 AU Dist [0.984/1.017] Sun-Moon distance -------------------------------------------------------------------------------- Note (1): This column includes recent mission instruments defined as follows: SP = The Spectral Profiler on board the SELENE; IIM = The Chang'E-1 Interference Imaging Spectrometer; M^3^ (OP1B) = The Optical Period 1B of the Moon Mineralogy Mapper; M^3^ (OP2A) = The Optical Period 2A of the Moon Mineralogy Mapper; M^3^ (OP2C1) = The Optical Period 2C1 of the Moon Mineralogy Mapper. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 I4 nm lambda [450/2395] Wavelength 6- 11 F6.3 W/m2/sr/um Rad5 [1.24/18.824] Radiance for the measurement site 5 13- 18 F6.3 W/m2/sr/um Rad6 [0.944/13.202] Radiance for the measurement site 6 20- 25 F6.3 W/m2/sr/um Rad7 [0.658/10.209] Radiance for the measurement site 7 27- 32 F6.3 W/m2/sr/um Rad8 [1.102/13.488] Radiance for the measurement site 8 34- 38 F5.3 --- Refl5 [0.044/0.13] Reflectance for the measurement site 5 40- 44 F5.3 --- Refl6 [0.041/0.131] Reflectance for the measurement site 6 46- 50 F5.3 --- Refl7 [0.034/0.102] Reflectance for the measurement site 7 52- 56 F5.3 --- Refl8 [0.029/0.101] Reflectance for the measurement site 8 -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Tiphaine Pouvreau [CDS] 10-Dec-2018