DWTS (Doppler Wind and Temperature Sounder) Measurements: Advantages, challenges and in-orbit calibration solutions Larry L. Gordley, Benjamin T. Marshall, Dave Fritts GATS Global Atmospheric Technology and Science, Inc. 11864 Canon Blvd., Suite 101, Newport News, VA 23606 Amal Chandran LASP Laboratory for Atmospheric and Space Physics, Boulder CO Richard L. Lachance GPI Gas Plume Imaging, Québec Canada 2016 International Satellite Program in Research and Education (INSPIRE) Workshop National Central University (NCU), Taiwan, Thursday, July 21 Session INSPIRESat-1: CubeSat mission to study the middle and upper atmosphere Slide 1
DWTS What is it? A Simple IR Camera observing through a gas cell Images the limb (starboard or port) with 20 FOV Uses cell gas as an absorption filter to scan the atmospheric emission NO channel cell transmission 13 CO 2 channel cell transmission! 1 1 0.8 0.8 transmittance 0.6 0.4 transmittance 0.6 0.4 0.2 0.2 0 0 a) 1830 1840 1850 1860 1870 wavenumber (cm -1 )! b) 2255 2260 2265 2270 2275 2280 2285 wavenumber (cm -1 )! Slide 2
What is DWTS? 6U: 2 (30 cm 10 cm 10 cm) DWTS single Chan. SWAP Size: 6U 0.3 Gbits/day Mass: 7 kg Power:14 W DWTS viewing geometry Cubesat demo version Slide 3
First camera concepts (SDL) Original single telescope two-channel design. Final three independent cameras DWTS instrument package. Slide 4
DWTS What can it do? Infer wind (two vectors), and temperature simultaneously From cloud-top to over 200 km Day and night If forecast value is as experts claim, the market for the data is enormous No other known technique can approach this capability Slide 5
Limb emission example Limb radiance in the DWTS Nitric Oxide channel at 5.3 μm Atmosphere only Slide 6
Doppler Spectroscopy One emission line example We stare at air parcel as satellite passes it. Its spectrum is Doppler shifted from blue to red. Gas cell absorption line Atmospheric emission line (viewed 10 forward, hence blue shifted) width ~ T A frequency Signal width ~ signal width of is produced signal yields as air parcel temperature passes T A +T G The shaded area is directly proportional to cell gas concentration 0 Doppler shift (view angle) Slide 7
Doppler Spectroscopy NO doublets produce multi-peak signal gas-cell absorption from NO doublet Atmospheric emission from NO doublet Doppler scan frequency Doppler scan produces triple-peak signal Signal Doppler shift (view angle) Slide 8
DWTS coverage Comparison to existing technology Current measurements provide inadequate altitude, and day/night coverage * Note that altitudes denoted by A or B will not be covered by this single channel (only NO) path finder instrument Slide 9
Global coverage Future constellation could provide dense coverage DWTS daily lat-lon & LT sampling on 6 COSMIC-2 SC at 800 km and 72 inclination. Slide 10
Challenges Power and Cooling (articulate bus, not solar panels) Vertical signal gradients Manage 3 to 4 orders of magnitude across the FPA PSF calibration in orbit High space view scans for offsets Stray light calibration and removal Lunar scans over the FOV Solar scans just off FOV FPA fixed pattern noise (flat-field with limb scans and down-looks) Pixel non-linearity (redundant lab techniques, on-orbit verification) Vibration effects (first look indicates only blurring) On-board data processing and management pixel aggregation and averaging Preservation of information Slide 11
Limb emission example Limb radiance in the DWTS Nitric Oxide channel at 5.3 μm Atmosphere with perfectly resolved moon and sun (no stray light or off-axis energy) Slide 12
Limb emission example Space view Moon and sun in place, without stray light Slide 13
Limb emission example Space view, with stray-light including sun just outside of FOV Slide 14
Calibration Nearly all performed in orbit Primary Secondary CALIBRATION OBJECTIVE Linearity Absolute Response Spectral Bandpass Cell Calibration Dark Current Read-out Nosie Timing Noise Flat Field Glare (Stray light) Reflection (Stray light) Blooming Total Noise FOV Polarization SBN SKE ITE Cold BB Comb Moon Sim Sun Sim FTS Int Gas Cell Ext Gas Cell Polarizer PSF In Orbit Moon DIP analysis Spectral DIP analysis Cold Space Cold space Cold space Limb & Moon scans Sun scans Moon scans moon scans cold space moon scans Moon Cold space Cold space Cold space Limb & Moon scans Sun scans Moon scans Moon (sun?) scans Cold space Moon scans Primary test Secondary test Throughput Point Spread Func Image Distortion moon obs moon scans Moon & scans Moon obs Moon scans limb Moon & limb scans Slide 15
DWTS Advantages DIP Measurement has intrinsic advantages (Spatial resolution, S/N, offset effects) i Absolute radiance calibration unnecessary (But, moon could provide) No spatial scale error (Relative pixel positions fixed) Stray light source-function known, and continuously measured No moving parts except cooler (except cooler) Gas filter fixed, known (Doppler broadening), and continuously calibrated In-orbit calibration of stray light and image distortion (Moon and Sun) Flat fielding from vertical scans, or down-looking in different FOV orientations Cooling and power optimization due to FOV orientation flexibility Slide 16
Summary DWTS, a leap in observation of upper atmosphere dynamics! Never been done! Low cost, elegant, and nearly trivial (relative to past techniques). New challenges, especially in calibration and data management. Enabled by modern FPAs, ADCS, processors and telemetry. No technical barriers, but stretches the bounds of cubesats. A weather forecaster s bonanza, if we can do it. Slide 17
GATS Global offering Solar Rays GEO: GRIPS, monitor Global GHG LEO: DWTS / T-STAR / HATS / SABER-I, monitor upper atmosphere wind, temperature, and gravity waves Downlink data to ground stations High altitude winds & temperature profiles Beams down data to Loon PIGC grid monitor GHG emission on global scale Airborne DAGR Mobile units detects & quantifies 2016 INSPIRE Workshop July 20 22, NCU,plumes Taiwan Slide 18
Available brochure Available upon request Slide 19
Backup slides Slide 20
INSPIRESat-1 Preliminary design work on INSPIRESat-1 started in January 2015 The first INSPIRE mission is proposed to be a six-unit (6U) cubesat carrying the Doppler Wind and Temperature Sounder (DWTS ) instrument DWTS will be co-developed by LASP, GATS Inc., and Brandywine Photonics The 6U spacecraft will be co-developed by LASP, IIST, and NCU The DWTS instrument utilizes an infrared camera to measure Doppler shifts and widths of nitric oxide (NO) emission spectra using gas correlation in the upper stratosphere (30 50 km), mesosphere, and lower thermosphere region (95 200+ km) Slide 21
INSPIRESat-1 Measurements are performed with a simple radiometer that images the limb emission of nitric oxide near 5.3 μm The goal for the instrument is to make simultaneous day and nighttime measurements of wind and temperature in the upper stratosphere and mesosphere/lower thermosphere (MLT) region for the first time Slide 22
DWTS How does it work? It scans atmospheric spectral emission features Scan is performed with gas cell spectra generated by same gas The scan is induced by the Doppler shift of limb emission as it passes through the 20 FOV The DIP (Doppler Integrated Pass) signal analyzed for wind, temperature, and cell content Wind from DIP minimum (along-sight) and scale (along track) Temperature from DIP width Cell content from normalized DIP area Slide 23
((Summary long version)) DWTS is a gas-filter correlation radiometer using a new approach with proven technology. It measures Doppler shifts and widths of emission spectra of NO, N 2 O, and CO 2 by imaging the limb to the side of the spacecraft. A small constellation of microsatellites in low Earth orbit could provide the critical wind and temperature data for next generation weather, severe storm prediction, and space weather needs. DWTS extracts kinetic temperature and horizontal wind vectors with unprecedented precision using a dramatically smaller, cheaper, and more accurate instrument than any competing solution. Furthermore, DWTS provides complete altitude and local-time coverage, in contrast to the partial coverage from previous or existing instruments, all of which are very expensive. Slide 24
Once funded, this instrument will leapfrog everything else with inexpensive (simple, no moving part) hardware and outstanding performance, This concept represents a revolution for anybody willing to take that risk Slide 25
Advantages Continuous day and night observations Imaging of the limb on both sides of the spacecraft Extended altitude coverage from 17 to 200 km Higher for stronger solar conditions or solar storms Dramatically better resolution: 2 3 km in altitude and 10 km along track Exceptionally high precision: ±2 K in temp. and ±2 m/s in wind speed On-board processing is simple frame averaging and pixel aggregation Small, simple, static, low mass, power, and much lower cost compared to satellite instruments like HRDI, TIDI, WINDII, DASH, OSIRIS, MLS, NIR, etc. Slide 26
Benefits Full 3D daily definition of stratosphere and mesosphere (for NWP) Full 3D definition of V, T, tides, and planetary waves in MLTI every orbit Global characterization of important small-scale gravity wave MLTI dynamics and influences (key GW parame-terization contributions) Assimilation and improvement of weather, climate, and Space Weather Support of other atmospheric science goals, environmental context for large majority of ground-based measurements Forecasting improvements and science never before possible None of this was possible with previous technology and instrumentation Slide 27
DWTS Design Parameters Parameter Detectors Gas cells spectral bandpasses Value Static, moderately cooled, Mid-IR cameras (4.6 5.4 μm) NO (high alt.): 1851 ±22 cm 1 13 CO 2 (mid alt): 2270 ±12 cm 1 N 2 O (low alt): 2165 ±10 cm 1 Field of View (FOV) 20 20 Aperture diameter 5 cm Focal length 5 cm Attitude knowledge yaw ±0.5 arcmin ; roll ±2.0 arcmin ; pitch ±1.0 Attitude Control ±1 all axes Jitter < 1 arcmin amplitude Angular drift < 3.0 arcsecs/sec all axes Spacecraft velocity knowledge ±1.0 m/sec One sided 3 channel SWAP Data rate Two sided 3 channel SWAP Data rate Pathfinder 6U (10 20 30 cm) ; 7 kg ; 7 W 225 Megabits/day Operational 9U (10 30 30 cm) ; 10 kg ; 10 W 450 megabits/day Slide 28