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 nsugimot@nies.go.jp

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.)

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.

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)

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

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

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)

Retroreflector In Space Experiment (5) Efficiency discussion The efficiency of the round-trip transmission to RIS was 10-11 to 10-8 using the 1.5-m satellite-tracking telescope with a transmitting beam divergence of 100 μrad. Retroreflector In Space Experiment (5)

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

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 10-11 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.

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

Earth-to-satellite DCS

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?

K. C. Cossel, et al., “Open-path dual-comb spectroscopy to an airborne retroreflector,” Optica 4, 7, 724-728 (2017). UAV borne retroreflector DCS paper Efficiency of round-trip optical transmission ~ 10-2, Wavelength 1.55-1.66 μm, Output power ~ 5mW. Target gas CO2, CH4, H2O  ~ 50 W is required for EtoS symmetric DCS with low orbit satellite?

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: 1.6-1.7 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

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.

Thank you

I. Coddington, N. Newbury, and W I. Coddington, N. Newbury, and W. Swann, “Dual-comb spectroscopy,” Optica 3, 4, 414-426 (2016).

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.