1. National Institute for Environmental Studies, Tsukuba, Japan
CLRC2018 Okinawa, 19 June 2018 (16:30-16:50)
A comb heterodyne receiver on a geosynchronous satellite? for long-path absorption measurements of atmospheric trace gases: a feasibility study
Nobuo Sugimoto
National Institute for Environmental Studies, Tsukuba, Japan

2. Contents
Concept of earth-to satellite laser long-path absorption measurements
The experiment using a retroreflector on a polar-orbit satellite (the Retroreflector in Space Experiment with ADEOS in 1996).
Earth-to-satellite laser long-path absorption spectroscopy using a detection system on the satellite
Discussion on the efficiency of optical transmission.
Feasibility of applying symmetric or asymmetric Dual Comb Spectroscopy. (In the asymmetric earth-to-satellite DCS, a comb heterodyne receiver is used on the satellite.)

3. Hinkley’s book
E. D. Hinkley ed., Laser Monitoring of the Atmosphere (Springer-Verlag, 1976), p. 288.
The earth-to-satellite laser long-path absorption method has potential advantages compared with the passive methods using solar radiation in accuracy, measurement frequency, and obviously in the nighttime measurement.

4. Retroreflector In Space Experiment (1)
Satellite movement
~ 7km/s
ADEOS (1996)
Polar orbit
Altitude ~ 800km
Large velocity aberration (60 μrad at max.) and Doppler shift (1.3 GHz at max. at 10 μm)
Retroreflector In Space Experiment (1)

5. Retroreflector In Space Experiment (2)
ADEOS 1996
Hollow cube-corner retroreflector having a curved mirror surface was developed
Retroreflector In Space Experiment (2)

6. Retroreflector In Space Experiment (3)
Method for measuring spectrum using the Doppler shift of the reflected beam was used.
Retroreflector In Space Experiment (3)

7. Retroreflector In Space Experiment (4)
Reflection from RIS in orbit
transmitted
1.5-m tracking system at CRL
RIS
received
Transmitted and received CO2 laser pulses
Single-mode TEA CO2 lasers
Measured spectrum of ozone
Retroreflector In Space Experiment (4)

8. Retroreflector In Space Experiment (5)
Efficiency discussion
The efficiency of the round-trip transmission to RIS was to 10-8 using the 1.5-m satellite-tracking telescope with a transmitting beam divergence of 100 μrad.
Retroreflector In Space Experiment (5)

9. Earth-to-satellite laser long-path absorption system using a detection system on the satellite
　　　　　　　　　　　　　　　　　　　　　　　　　　(Sugimoto 1987)

10. Optical transmission efficiency is higher
Earth-to-satellite laser long-path absorption system using a detection system on the satellite
Optical transmission efficiency is higher
Large satellite tracking system is not required
Distance to Satellite
Transmitted Beam Divergence (full angle), and Diameter of Receiver on Satellite
Optical Efficiency
36,000 km
100 μrad, 20 cm
~ 3 x 10-9
1,000 km
100 μrad, 10 cm
~ 1 x 10-6
Comparable to Lambertian hard target with 100% reflectivity
at 1 km,
with 10-cm receiver
at 50 m,
with 10-cm receiver
(The efficiency in the RIS experiment was to 10-8)
Pulsed laser based methods (e.g. double pulse differential absorption method) are feasible.
How about applying Dual-Comb Spectroscopy?
Measurement protocol may be standardized easier with DCS.

13. Symmetric dual comb spectroscopy
Symmetric DCS
Symmetric dual comb spectroscopy
(self-scanning FTS)
Comb + FTS

14. Earth-to-satellite DCS

15. How much output power is required for the comb?
Advantage
Problem
Symmetric DCS
Simple direct detection receiver
Sensitivity at low signal level
Asymmetric DCS
High sensitive (Multi heterodyne detection)
Control of onboard comb local oscillator
Accurate pointing of onboard receiver
Large Doppler shift
Comparison of Symmetric and Asymmetric DCS
Table ?
 Difficult with geosynchronous ?
 Difficult with low orbit
 Difficult with low orbit
How much output power is required for the comb?

16. K. C. Cossel, et al., “Open-path dual-comb spectroscopy to an airborne retroreflector,” Optica 4, 7, (2017).
UAV borne retroreflector DCS paper
Efficiency of round-trip optical transmission ~ 10-2,
Wavelength μm, Output power ~ 5mW.
Target gas CO2, CH4, H2O
 ~ 50 W is required for EtoS symmetric DCS with low orbit satellite?

17. Rough estimation showed the required power is
~ 1 mW per tooth for both symmetric DCS system with low orbit satellite and asymmetric DCS system with geosynchronous satellite.
Wavelength: μm
Target gas: CO2, CH4, H2O, HDO, 13CO2
Development of high power near-infrared frequency comb with optimized envelope spectrum
Symmetric DCS experiment using a hard target is good feasibility demonstration for Earth-to-Satellite measurements

18. Conclusions
A comb heterodyne receiver on a geosynchronous satellite? ………..
Earth-to satellite long-path absorption method having a detection system on the satellite is efficient. Optical transmission efficiency is comparable to hard target long-path absorption system.
Pulsed laser differential absorption methods are feasible.
The use of DCS is attractive because the measurement protocol can be standardized easier.
High-power optical frequency comb is needed. The envelope spectrum should be optimized for trace gas measurement.
Experiments on symmetric DCS using hard target reflection will be a good feasibility study of earth-to-satellite measurements.
Having a direct detection receiver on a small low-orbit satellite would be useful for further technical demonstration.

19. Thank you

20. I. Coddington, N. Newbury, and W
I. Coddington, N. Newbury, and W. Swann, “Dual-comb spectroscopy,” Optica 3, 4, (2016).

21. Hinkley’s book
E. D. Hinkley ed., Laser Monitoring of the Atmosphere (Springer-Verlag, 1976), p. 288.
The earth-to-satellite laser long-path absorption method has potential advantages compared with the passive methods using solar radiation in accuracy, temporal resolution, measurement frequency, and obviously in the nighttime measurement.