Cadence Payne, Angela Crews, Kerri Cahoy, Paul Serra, Alexa Aguilar, Peter Grenfell, John Conklin, Haeyoung Choi

Laser Crosslink Atmospheric Sounder

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Presentation Overview● Motivation● Approach● Measurement Assessment

○ Bending angle■ Temperature profiles

○ Differential wavelength■ Water vapor concentration

● CubeSat Demo Concept● Conclusions

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Motivation● Thunderstorms convectively inject water vapor into the upper

atmosphere [1]● Increase in water vapor and increase in temperature in the upper

atmosphere can deplete ozone [1]○ Decreased ozone = increased UV exposure

● Climate change can cause more storms, and decrease ozone

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Approach● Want to measure water vapor and temperature

in the upper atmosphere○ Need high vertical resolution from 10 km to

25 km altitude [1]

● Laser crosslinks can provide both concentration and temperature○ New concept: Bending angle-based laser

occultation retrieval measures temperature○ Differential wavelength intensities measure

concentration

● Can this be demonstrated with a smallsat platform at low cost?○ Low power transmitter (< 1W)○ CubeSat form factor (6U, 12U, etc.)○ LEO Orbit C. Payne

M. Long

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● Measure bending angle directly by tracking laser beam mispointing● Precision cm-level ranging supports geometry and orbit determination

Laser Occultation vs. GPS Radio Occultation

W. Schreiner

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A. Marinan, C. Payne

Novel Approach to Laser Occultation ● Laser occultation can concurrently

measure temperature profiles and water vapor concentration

● Previous concepts use GPS RO for profiles and laser occultation only for concentration [2]

● We use precision pointing and ranging in order to measure temperature profiles without GPS RO

6PV = n RT

Density n relates to index of refraction and bending

Measuring Bending Angle

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MEMS FSMs are relatively linear and well-behaved over temperature.

Fine pointing stage can be used to record bending angle precisely.

FSM Resolution: 0.137 arcsec

K. Riesing H. Yoon

Upper Atmosphere MissionsMission Horizontal/Vertical

Resolution Science Measurements Notes

LCAS < 250 m (vertical) Concurrent high resolution temperature and concentration

Mission in development

ESA ACCURATE [2]

1-2 km (vertical) 10 trace species; line of sight wind velocity, temperature, pressure and humidity profiles

Concept study from 2007Relies on GPS RO for profiles, uses laser for concentration

NASA SEAC4RS [4,5]

< 0.5 km In-situ measurements of atmospheric composition and aerosol properties

Airborne flight missionEarth’s radiation budget and tropospheric chemistry

NEXRAD [6,7] 1 km (reflectivity) Reflectivity, spatial location and distribution, high-resolution moisture measurements

Ground based coherent Doppler S-band radar system

Aura Microwave Limb Sounder [3]

2-3 km (H2O only) 15 trace species, cloud ice, temperature, geopotential height

Space flight missionStratospheric ozone

ACE-FTS [8,9] 1 km to < 10 km (horizontal)

Solar spectrum. Composition of troposphere, stratosphere and polar mesospheric clouds.

Space flight missionSolar occultation 8

Presentation Overview● Motivation● Approach● Measurement Assessment

○ Bending angle■ Temperature profiles

○ Differential wavelength■ Water vapor concentration

● CubeSat Demo Concept● Conclusions

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Wavelength AssessmentMODTRAN Geometric Configuration

A. Crews

● Intensity on the continuum and near the absorption features of the spectrum can measure water vapor concentration

● Need paired, proximal wavelengths○ One constant and one with attenuation

in 1500-1600 nm range● Used MODTRAN to assess the effect of

water vapor in the atmosphere based on lasercom crosslink geometry

● Wavelength selection:○ Adjust scale value of water vapor (1x,

2x, 3x) at tangent heights of 10 km, 15 km and 20 km

○ Flexible wavelength selection for probing other species 10

1504 nm and 1508.8 nm show satisfactory changes in attenuation1550.4 nm is identified as a stable reference wavelength

Wavelength assessment

A. Crews A. Crews

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Wavelength assessment

Rain and clouds will not negatively affect measurements of the upper atmosphere

Change in Transmittance for Selected Wavelengths at 10, 15, and 20 km

A. Crews A. Crews

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CubeSat Demo: Leverage CLICK Platform● Coarse and fine pointing stage

○ Fine pointing stage to measure bending angle

○ Retrieve temperature profiles

● Precision ranging with Chip Scale Atomic Clock (CSAC) and Time to Digital Converter (TDC)

● Modify tx to quickly alternate two wavelengths○ 1504 nm or 1508 nm○ 1550 nm (reference)

M. Long, P. Grenfell

CLICK fine pointing optical system

LPF

Diff AMP

ADC

LPF Comparators

From APD

Test Input

TDCLatches

FPGA

PLLCSAC

TCXO

CLICK Receivers

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CLICK Pointing and Ranging works for LCAS● Lasercom crosslink FWHM divergence angle:

14.6 arcsec; Beacon crosslink FWHM divergence angle: 0.75 degrees (13 mrad)

● CLICK precision ranging:○ Better than 50 cm (~1.6 ns)○ Pulse repetition rate of up to 10 MHz

● Approach for LCAS:○ Initial acquisition of beacon laser on

CMOS camera○ Closed-loop inertial tracking○ Fine pointing and tracking○ Internal calibration laser spot position

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Fine Pointing Testbed with ResultsP. Grenfell, H. Yoon (MIT) [11]

Summary and Future Work● Science Analysis:

○ Refine vertical resolution performance ○ Atmospheric contribution from pointing error○ Temperature profile retrievals from noisy bending angles○ Composition retrieval from atmospheric attenuation in two

wavelengths with noise

● Mission Design:○ Refine wavelength and power○ Orbit geometry and phasing (drag vs. propulsion)○ Use of new technology such as laser frequency combs for

composition/concentration measurement and ranging○ Power assessment, TRL maturation, size, weight and power

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Related talks at SmallSat and AcknowledgmentsAcknowledgements● LCAS Team and PI Kerri Cahoy● John Conklin’s group at the University of Florida for their efforts on precision timing● SmallSat organizers and judges

Related InfoSession XII: Advanced Technologies II, 11:30 AM“Integration & Testing of the Nanosatellite Optical Downlink Experiment” (A. Aguilar)

Poster Session II:“Time-To-Digital Converter vs. Analog-To-Digital Converter & Matched Filter Performance in Nanosatellite Optical Receivers” (A. Aguilar)“Laser Communication Crosslinks for Satellite Autonomous Navigation” (P. Dave)

University Booth:Massachusetts Institute of Technology University Booth U4

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Questions?

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BACK UP

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References[1] J. Anderson, D. Weisenstein, K. Bowman, et al., “Stratospheric ozone over the united states in summer linked to observations of convection and temperature via chlorine and bromine catalysis,” PNAS Early Edition (2017).[2] Kirchengast and Scheweitzer, “ACCURATE LEO-LEO Infrared Laser Occultation Initial Assessment: Requirements, Payload Characteristics, Scientific Performance Analysis, and Breadboarding Specifications,” WegCenter/UniGraz Technical Report (2007).[3] J. Waters, L. Froidevaux, R. Harwood, et al., “The earth observing system microwave limb sounder (eos mls) on the aura satellite,” IEEE Transactions on Geoscience and Remote Sensing 44 (2006).[4] J. Anderson, D. Weisenstein, K. Bowman, et al., “Stratospheric ozone over the united states in summer linked to observations of convection and temperature via chlorine and bromine catalysis,” PNAS Early Edition (2017).[5] https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015JD024297[6] Heiss, William H., et al. "Nexrad: next generation weather radar (WSR-88D)." Microwave Journal, Jan. 1990, p. 79+. Academic OneFile, Accessed 3 Aug. 2018[7] Roberts, R.D., F. Fabry, P.C. Kennedy, et al., “Real-Time Retrieval of High-Resolution, Low-Level Moisture Fields from Operational NEXRAD and Research Radars,” Bull. Amer. Meteor. Soc., 89, 1535–1548, 2008[8] FrankHase, LloydWallace, Sean D.McLeod, et al., “The ACE-FTS atlas of the infrared solar spectrum,” Journal of Quantitative Spectroscopy and Radiative Transfer, Volume 111, Issue 4, 521-528, March 2010[9] https://earth.esa.int/web/guest/data-access/view-data-product/-/article/scisat-1-ace-fts-and-maestro[10] “Ohio state university astronomy department.” http://www.astronomy. ohio-state.edu/pogge/Ast161/Unit5/atmos.html.[11] Yoon, H., “Pointing System Performance Analysis for Optical Inter-satellite Communication on CubeSats,” Ph.D Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113743

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Power assessment

Can we make this measurement using

COTS components? [2]

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Mission Horizontal/Vertical Resolution Data Products Key Differences between Mission and LCAS

LCAS < 250 m (vertical) Water vapor concentration in UTLS and temperature profiles

ESA ACCURATE [2] 1-2 km (vertical) 10 trace species; LOS wind velocity; SNR; temperature, pressure and humidity profiles

Reliant on LEO-LEO RO for extracting temperature, pressure and humidity.Probing 10 trace species

NASA SEAC^4RS [4, 5] < 0.5 km In situ measurements of atmospheric composition, aerosol properties and impact on clouds, performance metrics of new instruments

Survey. In situ measurements from aircraft & balloons with array of instruments. Focused on Earth’s radiation budget and tropospheric chemistry.

NEXRAD [6,7] 1 km (reflectivity) Reflectivity measurements, spatial location and distribution, storm relative velocity, high-res moisture measurements

Fully coherent doppler S-band radar system.

Aura Microwave Limb Sounder [3]

2-3 km (H2O only at 316 hPa tropopause)

15 trace species, cloud ice, temperature, geopotential height

Focused on chemistry of stratospheric ozone. Microwave sounder using spectrometers and radiometers

ACE-FTS [8, 9] 1 km to < 10 km (horizontal)

Composition of troposphere, stratosphere and polar mesospheric clouds. Solar spectrum.

Fourier transform spectrometer. Tangent heights between 5-150 km. Solar occultation measurements to infer terrestrial atmospheric composition.

PAT System-ConOps

RF Crosslink Beacon CrosslinkBeacon & Comms

Crosslink

Figure Credit: P. Grenfell22

CLICK Link AnalysisTable 2: Overview of key parameters in the CLICK inter-satellite link analysis.The link analysis is completed for 20

Mbps data rate and 1537/1565 nm wavelengths.

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CLICK Beacon to Camera Budget

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LCAS Beacon to Camera Budget

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CLICK Beacon to Quadcell Link Budget

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LCAS Beacon to Quadcell Link Budget

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CLICK Pointing Summary (P. Grenfell)

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Laser Divergences:

•Lasercom crosslink FWHM divergence angle: 14.6 arcsec (70.8 urad)

•Beacon crosslink FWHM divergence angle: 0.75 degrees (2700 arcsec)

PAT Analysis & Test Results:

•Coarse Pointing & Tracking Capability (Simulation): 97.8 arcsec (half-angle)

•Fine Pointing Capability (Simulation): 0.538 arcsec (half-angle)

•Fine Pointing Capability (Hardware): 2.382 arcsec (half-angle)

•Improvement over Coarse Pointing: 41 to 181 times

•Significant margin (67% to 93%) for opto-mechanical errors

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Atmospheric transmission spectrum of air. Near infrared transmission spectrum, showing H2O, CO2, O3, and CH4 [10].