11:00 AM - 11:15 AM
[SGD02-08] Compact, Low-Cost, Multipurpose SLR System Omni-SLR (2): Time Comparison Using Optical Pulse Transmission Between Two Stations
Keywords:SLR, Time Transfer
SLR (Satellite Laser Ranging): Overview and Applications Beyond Ranging
Satellite Laser Ranging (SLR) is a geodetic technique that measures the distance between a ground station and a satellite. This is achieved by transmitting laser pulses from the Earth's surface to a satellite, where the laser is reflected by Corner Cube Reflectors (CCRs) mounted on the satellite, and measuring the round-trip time of the light signal. Currently, the Ishigaki Geodetic Observatory is conducting repeated tests aimed at deploying a compact and cost-effective SLR system, the Omni-SLR.
This presentation highlights one application of the Omni-SLR beyond SLR measurements: the comparison of clocks between two locations. High-precision clocks, such as hydrogen maser atomic clocks, cesium atomic clocks, and optical lattice clocks, are widely available worldwide and are also used in determining Japan Standard Time. However, comparing clocks located far apart with sub-nanosecond precision has been challenging due to the limited accuracy of GNSS-based methods and the need for specialized equipment like optical fibers or VLBI systems.
Our plan is to enable time comparison using the compact and cost-effective Omni-SLR. To achieve this, in addition to the primary SLR station (Station A) used for ranging purposes, we have established a second, simplified station (Station B) that maintains equivalent functionality for time comparison purposes.
The two SLR stations simultaneously conducted laser ranging on the same target. When installed in close proximity, modifications to the optical system were necessary to ensure that the transmitted beam was directed at the target by offsetting the pointing directions of the transmitting and receiving telescopes. While conventional SLR focuses on self-return signals (e.g., A→A or B→B), we enabled observations of cross-station pulses (e.g., A→B and B→A). Statistical analysis of these time-series data demonstrated the ability to compare with an accuracy of a few picoseconds. Preliminary results from comparisons between GNSS signal generators yielded an Allan deviation of approximately 2–3 x 10^-10 at 1 second.
Additionally, for clock comparisons between two locations, we directly compared the 1 Pulse Per Second (PPS) signals from two types of GNSS signal generators without using optical pulse transmission. Statistical analysis was performed on this time-series data as well, allowing a comparison of the Allan deviation behavior for optical pulse transmission and direct PPS signal comparison. This confirmed that the precision of clock comparisons was not degraded using optical pulse transmission.
Furthermore, we are advancing comparisons with different types of GNSS signal generators and hydrogen masers used for VLBI by the Geospatial Information Authority of Japan.
Satellite Laser Ranging (SLR) is a geodetic technique that measures the distance between a ground station and a satellite. This is achieved by transmitting laser pulses from the Earth's surface to a satellite, where the laser is reflected by Corner Cube Reflectors (CCRs) mounted on the satellite, and measuring the round-trip time of the light signal. Currently, the Ishigaki Geodetic Observatory is conducting repeated tests aimed at deploying a compact and cost-effective SLR system, the Omni-SLR.
This presentation highlights one application of the Omni-SLR beyond SLR measurements: the comparison of clocks between two locations. High-precision clocks, such as hydrogen maser atomic clocks, cesium atomic clocks, and optical lattice clocks, are widely available worldwide and are also used in determining Japan Standard Time. However, comparing clocks located far apart with sub-nanosecond precision has been challenging due to the limited accuracy of GNSS-based methods and the need for specialized equipment like optical fibers or VLBI systems.
Our plan is to enable time comparison using the compact and cost-effective Omni-SLR. To achieve this, in addition to the primary SLR station (Station A) used for ranging purposes, we have established a second, simplified station (Station B) that maintains equivalent functionality for time comparison purposes.
The two SLR stations simultaneously conducted laser ranging on the same target. When installed in close proximity, modifications to the optical system were necessary to ensure that the transmitted beam was directed at the target by offsetting the pointing directions of the transmitting and receiving telescopes. While conventional SLR focuses on self-return signals (e.g., A→A or B→B), we enabled observations of cross-station pulses (e.g., A→B and B→A). Statistical analysis of these time-series data demonstrated the ability to compare with an accuracy of a few picoseconds. Preliminary results from comparisons between GNSS signal generators yielded an Allan deviation of approximately 2–3 x 10^-10 at 1 second.
Additionally, for clock comparisons between two locations, we directly compared the 1 Pulse Per Second (PPS) signals from two types of GNSS signal generators without using optical pulse transmission. Statistical analysis was performed on this time-series data as well, allowing a comparison of the Allan deviation behavior for optical pulse transmission and direct PPS signal comparison. This confirmed that the precision of clock comparisons was not degraded using optical pulse transmission.
Furthermore, we are advancing comparisons with different types of GNSS signal generators and hydrogen masers used for VLBI by the Geospatial Information Authority of Japan.