Near-infrared photometry of the Moon’s surface with passive radiometry from the Lunar Orbiter Laser Altimeter (LOLA)
Ryan Walker
Introduction
LOLA's passive radiometry mode was not in the original instrument mission goals, but was developed in-flight as an alternative mode when laser altimetric ranging is not feasible. In this mode, the solar photons within a bandpass of 1064.45 ± 0.35 nm that are reflected off the lunar surface and that are "noise" for altimetry become the signal. This allows LOLA to act as a 4-channel radiometer collecting data at 28 Hz (yielding a ~57 m along-track measurement separation for each channel) with a combined footprint diameter of ~120 m (~40 m for each channel) from 100 km altitude.This near-infrared dataset is unique because of its narrow bandwidth and precise geolocation, and is complementary to observations made by other instruments onboard LRO at other wavelengths, including the Diviner Lunar Radiometer Experiment (DLRE, thermal infrared), the Lunar Reconnaissance Orbiter Camera (LROC, visible-ultraviolet), and the Lyman-Alpha Mapping Project (LAMP, far ultraviolet).
The calibration procedure is fully described in:
Walker, R. T., Barker, M. K., Mazarico, E., Sun, X., Neumann, G. A., Smith, D. E., Head, J. W., & Zuber, M. T., 2024. Near-infrared photometry of the Moon’s surface with passive radiometry from the Lunar Orbiter Laser Altimeter (LOLA), submitted to Planetary Science Journal.
Data are provided in Apache Parquet file format, which allows efficient data compression and the ability to read only the columns of interest. Parquet files are readable by Python, R, Matlab, and many big data tools and specialized viewers.
The data are organized by mission phase (currently, LRO ES 14 through 108, 21 November 2013 – 19 November 2021). Filenames are in the form "lola_pasrad_{orbit}.parquet", where orbit (YYDDDHHMM) is labeled by the UTC time of the ascending node and is identical to the name of the corresponding LOLA Reduced Data Record (RDR). DDD is the 3-digit day of year.
Download each LRO_ES phase passive radiometry data from the following links (compressed, .tar.gz format):
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108.
Data Description
transmit_time (int64): Terrestrial Dynamic Time (TDT) at LRO in full seconds from the J2000 epoch.
transmit_time_sub (int64): Fractional seconds for transmit_time. The full TDT in seconds is transmit_time + transmit_time_sub / 232.
longitude (int32) : Planetocentric longitude (± 180°) of the full rate data point. Divide by 107 to obtain value.
latitude (int32): Planetocentric latitude of the full rate data point. Divide by 107 to obtain value.
raw_noise_count_{2, 3, 4, 5} (int32): Background noise for altimetry at detectors 2-5, used as passive radiometry signal. Raw noise counts include thermal noise (dark current), which is removed in the calibration process.
radiance_factor_{2, 3, 4, 5} (int32): Calibrated radiance factor (RADF or I/F) at detectors 2-5. Divide by 104 to obtain values.
radiance_factor_mean (int32): Average of RADF at detectors 2-5, used as the RADF value at each full rate data point. Divide by 104 to obtain value.
absolute_radiance (int32): Absolute radiance in W/m2/μm/steradian, adjusted for LRO-Sun distance using 647 W/m2/μm as the solar irradiance at 1 AU. Divide by 104 to obtain value.
incidence_angle (uint16): Angle between Sun-to-surface vector and surface normal. Multiply by 5 × 10-5 × 180° / π to obtain value in degrees.
emission_angle (uint16): Angle between LOLA-to-surface vector and surface normal. Multiply by 5 × 10-5 × 180° / π to obtain value in degrees.
phase_angle (uint16): Angle between Sun-to-surface and LOLA-to-surface vectors. Multiply by 5 × 10-5 × 180° / π to obtain value in degrees.
offnadir_angle (uint16): Angle from LRO nadir to boresight for central spot. Multiply by 5 × 10-5 × 180° / π to obtain value in degrees.
Data Usage Policy
Please cite the following references when using the product described above.Manuscript: Walker, R. T., Barker, M. K., Mazarico, E., Sun, X., Neumann, G. A., Smith, D. E., Head, J. W., & Zuber, M. T., 2024. Near-infrared photometry of the Moon’s surface with passive radiometry from the Lunar Orbiter Laser Altimeter (LOLA), The Planetary Science Journal, 5, 122. doi:10.3847/PSJ/ad4467
Dataset: Walker, R. (2024). Near-infrared photometry of the Moon’s surface with passive radiometry from the Lunar Orbiter Laser Altimeter (LOLA) [Data set]. NASA Goddard Space Flight Center Planetary Geodesy Data Archive. doi:10.60903/GSFCPGDA-LOLAPRAD2024.