Abstract
The Lunar Radar Sounder (LRS) onboard the KAGUYA (SELENE) spacecraft has successfully performed radar sounder observations of the lunar subsurface structures and passive observations of natural radio and plasma waves from the lunar orbit. After the transfer of the spacecraft into the final lunar orbit and antenna deployment, the operation of LRS started on October 29, 2007. Through the operation until June 10, 2009, 2363 hours worth of radar sounder data and 8961 hours worth of natural radio and plasma wave data have been obtained. It was revealed through radar sounder observations that there are distinct reflectors at a depth of several hundred meters in the nearside maria, which are inferred to be buried regolith layers covered by a basalt layer with a thickness of several hundred meters. Radar sounder data were obtained not only in the nearside maria but also in other regions such as the farside highland region and polar region. LRS also performed passive observations of natural plasma waves associated with interaction processes between the solar wind plasma and the moon, and the natural waves from the Earth, the sun, and Jupiter. Natural radio waves such as auroral kilometric radiation (AKR) with interference patterns caused by the lunar surface reflections, and Jovian hectometric (HOM) emissions were detected. Intense electrostatic plasma waves around 20 kHz were almost always observed at local electron plasma frequency in the solar wind, and the electron density profile, including the lunar wake boundary, was derived along the spacecraft trajectory. Broadband noises below several kHz were frequently observed in the dayside and wake boundary of the moon and it was found that a portion of them consist of bipolar pulses. The datasets obtained by LRS will make contributions for studies on the lunar geology and physical processes of natural radio and plasma wave generation and propagation.
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Abbreviations
- 1PPS:
-
1 pulse per second
- A/D:
-
Analog-to-digital converter
- AKR:
-
Auroral kilometric radiation
- ALSE:
-
Apollo Lunar Sounder Experiment
- BPF:
-
Band-pass filter
- CML:
-
Jovian System III central meridian longitude
- D/A:
-
Digital-to-analog converter
- DAM:
-
Decametric radiation
- DHU:
-
Data handling unit
- DSP:
-
Digital signal processor
- ECU:
-
Electric control unit, which is a controller of the solar array paddle
- EMC:
-
Electromagnetic compatibility
- ESW:
-
Electrostatic solitary wave
- FET:
-
Field effect transistor
- FFT mode:
-
One of observation mode of the WFC-H; the spectrum data are produced by the onboard software using the Fast Fourier Transform
- FIFO:
-
First-in first-out memory
- FMCW:
-
Frequency modulated continuous wave
- FPGA:
-
Field programmable gate array
- Ga:
-
Giga years ago
- GSE:
-
Geocentric solar ecliptic coordinate system
- HF:
-
High frequency; frequency range from 3 to 30 MHz
- HK:
-
House keeping status
- HOM:
-
Hectometric radiation
- HPF:
-
High-pass filter
- IF:
-
Intermediate frequency
- JAXA:
-
Japan Aerospace Exploration Agency
- LALT:
-
Laser Altimeter onboard the KAGUYA spacecraft
- LRS:
-
Lunar Radar Sounder
- LRS-A:
-
LRS antenna units
- LRS-E:
-
LRS main electronics unit
- LRS-P:
-
LRS preamplifier units
- LPF:
-
Low-pass filter
- MARSIS:
-
Mars Advanced Radar for Subsurface and Ionospheric Sounding
- MEX:
-
Mars Express
- MRO:
-
Mars Reconnaissance Orbiter
- NCO:
-
Numerically controlled oscillator
- NPW:
-
Natural plasma wave receiver; a passive receiver of LRS covering from 20 kHz to 30 MHz
- NPW-A:
-
NPW low-rate waveform mode; operation mode of NPW subsystem
- NPW-DS:
-
NPW dynamic spectra mode; operation mode of NPW subsystem
- NPW-PL:
-
NPW polarization mode; operation mode of NPW subsystem
- NPW-S:
-
NPW spectra mode; operation mode of NPW subsystem
- NPW-W:
-
NPW waveform mode; operation mode of NPW subsystem
- OBC:
-
Onboard computer
- PDC:
-
Programmable down converter
- PHASE mode:
-
One of observation mode of the WFC-H; the intensity and phase difference between two orthogonal components at each frequency point are transported to the ground
- PRF:
-
Pulse repetition frequency
- RF:
-
Radio frequency
- RGA:
-
Reiner Gamma magnetic anomaly
- RX1, RX2:
-
Receiver 1, Receiver 2
- SAR:
-
Synthetic aperture radar
- SDR:
-
Sounder observation
- SDR-A:
-
SDR low-rate waveform mode; operation mode of SDR subsystem
- SDR-W:
-
SDR waveform mode; operation mode of SDR subsystem
- SHARAD:
-
Shallow Radar
- SNR:
-
Signal to noise ratio
- SPLD:
-
South Polar Layered Deposits
- STEREO:
-
Solar Terrestrial Relations Observatory
- STP:
-
Solar Terrestrial Physiscs
- TC:
-
Terrain Camera
- TFG:
-
Transfer frame generator
- THR:
-
Terrestrial hectometric radiation
- TNR:
-
Thermal noise receiver; a spectrum receiver onboard WIND spacecraft
- TR:
-
Transmitter/receiver switch
- ULF:
-
Ultra low frequency; frequency range from 300 Hz to 3 kHz
- UT:
-
Universal time
- WAVE mode:
-
One of observation mode of the WFC-H; the down-converted and decimated signals of in-phase and quadrature components are sent as telemetry data
- WFC:
-
Waveform capture; a passive receiver of LRS covering from 100 Hz to 1 MHz
- WFC-DUMP:
-
A special mode of WFC receiver, in which waveform is once stored in the onboard memory and sent to the ground later by a DUMP command
- WFC-H:
-
WFC-High; a fast sweep-frequency receiver covering from 1 kHz to 1 MHz
- WFC-H-X:
-
X component of WFC-H receiver; differential signal between LRS-A1 and LRS-A3 antennas is fed to the WFC-H receiver
- WFC-H-Y:
-
Y component of WFC-H receiver; differential signal between LRS-A2 and LRS-A4 antennas is fed to the WFC-H receiver
- WFC-L:
-
WFC-Low; a waveform receiver covering from 100 Hz to 100 kHz
- WFC-L-X:
-
X component of WFC-L receiver; differential signal between LRS-A1 and LRS-A3 antennas is fed to the WFC-L receiver
- WFC-L-Y1:
-
Y component of WFC-L receiver; differential signal between LRS-A2 and LRS-A4 antennas, or single signal from LRS-A2 antenna is fed to the WFC-L receiver
- WFC-L-Y2:
-
Single signal from LRS-A4 is fed to the WFC-L receiver
- WFC-DSP:
-
A digital board for WFC receiver
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Ono, T., Kumamoto, A., Kasahara, Y. et al. The Lunar Radar Sounder (LRS) Onboard the KAGUYA (SELENE) Spacecraft. Space Sci Rev 154, 145–192 (2010). https://doi.org/10.1007/s11214-010-9673-8
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DOI: https://doi.org/10.1007/s11214-010-9673-8