The Variety of New Commercial Aircraft Sensors for Weather, Climate, and Air Quality Applications: Accuracy and Use Dr. Rex J. Fleming SpectraSensors, Inc. May 16, 2006
Time is right for a paradigm shift in observations for atmospheric science • Observational accuracy has not kept pace with advances in computers and modeling/analysis capabilities • Platforms that move on our planet can potentially make enormous contributions with continuous measurements in space/time. • If measurements are extremely accurate, then valuable in their own right and make satellite data (conventional or GPS related) more valuable (via Kalman filter, 4DDA, • or other optimization methods)
“Accurate” Environmental Data will Escalate in Value over Time • Weather and climate already impact about 1/7 of a 7 trillion dollar USA economy • Consider growth in 7 major socioeconomic areas: • Energy: largest single issue for USA and the world • Water: fresh water is 2nd largest issue for society • Food: average population increase only 1.1%/yr vs 1.7% past 30 yr • Transportation: major growth area (aviation impact already huge) • Weather impacts: (human health, safety, etc) vs 1.1% pop. growth • Climate change (global warming uncertainty vs energy conflict) • Construction and other: Population growth 1.1%/year • Value of “accurate” environmental data will double approximately every 6-8 years in future.
Commercial Aircraft create a paradigm shift in atmospheric observations – for the benefit of aviation and society Radiosondes: balloon launchs (2/day) have high vertical resolution; poor space and time resolution (500km, 1/day in many countries); do not serve high space /time requirements of aviation needs Satellites: global cloud images very useful, but profile data inaccurate; poor vertical resolution on T and q; little information from cloud winds Commercial aircraft: space/ time coverage from moving platforms provide unique data blend that helps merges all these data sets into a unifying whole; winds and water vapor more accurate 15 countries have organized national commercial aircraft programs; 18 more countries have programs in various stages of implementation The Next Generation Air Transportation System (NGATS) will depend on the aircraft measurements (commercial & possibly general aviation)
This Presentation Covers Three types of Sensors (all same architecture) 2nd generation Water Vapor Sensing System (WVSS-II) -- WVSS-II (current for commercial jets) in USA and Europe -- WVSS-III for turboprop a/c and all mobileplatforms below 25,000 ft -- Modified WVSS-II for upper troposphere and stratospheric research (Herriott cell inside; same size, but more expensive) Mobile Temperature Sensor (MTS) for better temperature from a/c and other mobile platforms Quantum cascade (QC) lasers for atmospheric trace gases
Emergence of mobile platforms [commercial aircraft (jets and turboprops), helicopters, unmanned aerial vehicles (UAVs), etc.] driven by: Convenience – mesoscale coverage in USA, over ocean with satellite communications, difficult/dangerous regions via UAVs Sensor accuracy – dramatic turn for the better with new technology Demand for more accurate data – socioeconomic demand is accelerating
History: WVSS-I Results and why RH by thin film rejected: www.joss.ucar.edu/wvss/
Why WVSS-I (RH sensor) Abandoned by FAA and NOAA/OGP 4 years of flight tests with UPS [Vaisala thin film sensor–best of radiosondes – has following known problems in measuring relative humidity (RH)] -- difficult to calibrate at very low and high RH values -- calibration changes over time -- sensor response time is very slow at cold temperatures -- sensor reads well over 100% when wet; cosmetic fix; takes time to dry Mach effect on aircraft bad for RH measurement (not for mixing ratio or dew pt.) -- amplifies sfc random error (5%) by factor: (3) for turboprops (17) for jets Found large changes between aircraft to aircraft over time -- limitation of thin film – each manufactured lot is different, and within each lot each radiosonde has to be calibrated individually -- results show average lifetime 6 months (based upon loss of sensitivity at upper levels) European Project MOSAIC (Measurement of Ozone by Airbus In-service Aircraft) -- 10 year effort of recording ozone and water vapor (using Vaisala thin film sensor) produced over 2500 over-ocean flights with 140,000 hours of data -- had to recalibrate the Vaisala sensor every month (Herman Smit, Germany)
Error analysis: Mach Number Effect If Mach # = 0.8, Ts = -60C = 213.15K then: Tprobe = Tstatic (1 + 0.2M 2) = Tstatic (1.128) = 240.43 Pprobe = Pstatic (1 + 0.2M 2) 3.5 = Ps(1.524) and: es, s (213.15) = 1.76 es, p (240.43) = 38.41 and from RHstatic = RHprobe (es,probe / es,static ) (Pstatic / Pprobe ) RHstatic / RHprobe = (es, probe/es, static)(Pstatic/Pprobe) = (38.41/1.76) / (1.524) = 14.32 z:/fleming/vgraphs/Error analysis.ppt
WVSS-II Sensor Technology: absorption spectroscopy – transmission of laser light through absorbing gas ( diode laser @ 1.37 micron) I0 I I = I0 exp ( - σ n L) I = intensity at detector I0 = initial intensity σn L = absorbance = α n = number density of gas L = path length σ = molecular absorbing cross section = σ ( μ P T )
WVSS-II on UPS B-757 8.89 cm Aircraft skin Inertial separator (inside, see Fig. 3) Cylindrical sampling tube Turbulence enhancer 24 cm Figure 2. Cross section of complete sampler
Installed System Photos Open Path Sensor WVSS-II Air Sampler
NOAA P3 Center Flight Section Chilled mirror overshoots
WVSS-II on UPS B-757 • Air Sampler: Flush mounted / low drag / no heater required • Diode laser, 20 year life, telecommunications standard • System weight (electronics box, cables, air sampler) < 7 lbs • Overall Box Dimensions 5.0” x 9.0” x 3.1”
Key Events in Operational WVSS-II Product History FAA Certification for B-757 cargo aircraft 12/04 UPS installation of 25 units 3/05 to 6/05 Early results (all on internet in real time) -- 3 of 4 errors proven fixed on subsequent installations -- 4th error fix proven in lab (being certified)– heated hose -- all units retrofitted after certification WVSS-II vs radiosonde in U. of Wisconsin tests 6/05 -- conducted by W. Feltz and R. Petersen Six units shipped to Germany for A320 certification 3/06 Airbus visit to SpectraSensors for final evaluation 5/06 -- European AMDAR requested Airbus consider the WVSS-II for all Airbus aircraft (considerable exchange) -- visit by Airbus staff for final check of manufacturing ability, quality control, and meeting schedules for deliveries
Simple Optical Layout of WVSS-II H2O Sensor (not to scale) Laser 12 cm each way Mirror Thermal Block Detector 24 cm optical absorption pathlength for measurements Note that there is a 0.5 cm path within optical head
1st Hardware change: Remove leak in optical head First 11 aircraft carried surface water vapor aloft Problem identified and solution found: -- profile comparison with radiosondes great, but some a/c always had 100% RH in upper trop. (most distressing because every decision has been driven to obtain accuracy in this very poorly measured portion of the atmosphere). -- connector to back of optical head was not truly hermetic allowing vapor behind a 1.0 cm path (compared to true measurement over a 24 cm path). -- natural gas water vapor sensors of SSI have better connector and 4X more desiccantin optical head (field proven 3+ years of lifetime) -- solution two fold: source found for true hermetic versions of sameconnector (tests indicate desiccant would last 200 years) and simple design changes in optical head allow 6X more desiccant.
2nd hardware change required: heated hoses Had debate three years ago about descent into very warm and humid conditions – would condensation be an impact (system or data) ? Impact issue was more about the system rather than the data -- heated hose was considered rather more complicated and system would flush any water on next ascent taxi -- now appears that the condensation does pull sufficient water vapor from the air sample to lower the mixing ratio (despite the fact that 2500 Joules per gram of water are released as heat to help reduce the condensation). Solution is same easy solution used by Randy May for NASA: same company makes heated hoses with a controller. Circuit keeps measurement cell at 35 C.
Summary of European Activity Concerning WVSS-II TheGerman Weather Service working with Lufthansa and Airbus will fund the certification of the A320 family of a/c (A319, A320, A321) The first 10 WVSS-II units will go on new A320 aircraft to be delivered to Lufthansa (5), Air New Zealand (1) Jet Star –Australia (2), and South African Airlines (2) Herman Smit (scientist with MOSAIC project has been testing the WVSS-II Electronics box in his lab – if they like, they will certify for A340 and put on 6-8 MOSAIC aircraft The European AMDAR group has asked Airbus to consider the WVSS-II as an optional product for all of their aircraft (they have come to SpectraSensors with detailed questions and are still evaluating)
Commercial Aircraft measurements of atmospheric temperature 8 years ago I first heard about problem – Qantas B-747 (3 sensors) 4 years ago I began thinking about the problem – subliminally 2 years ago I solved problem ,conceptually, and verified via complex simulations that it would work 6 months ago Randy May and I proved the concept at the U. of Washington wind tunnel While I believe the solution is proven by wind tunnel results and simulations, you and others will believe it only after actual flight tests in the next 6-8 months – of course! Today, you will hear some detail, not all; fully patent protected
Commercial Aircraft measurements of atmospheric temperature TT = TS ( 1 + 0.2 M 2 ) Measurements are: Indirect: avionics measure TT not TS (which we want) Affected by heated probe: outside a/c skin boundary layer, therefore FAA requires the Total Air Temperature (TAT) probe be heated Intrusive: measurement affected by environment over time -------------------------------------------------------------------------------------------- Solution: Measure TS directly Measure TS within boundary layer (no heater); isolate effect of friction and model that effect via singular value decomposition (SVD) Imbed sensors (2) within walls (5/1000 of inch) protected from environment
Four Requirements for a Successful Flush Mounted Temperature Sensor Location on fuselage with reasonably laminar flow Sensor housing thermally shielded with insulating gaskets (from external heat source (sun) and internal heat sources) Friction effects (thus isolated with above shielding) produce temperature increase modeled with a polynomial in Mach Number: ΔTF = A1 + A2 M + A3 M2 + A4 M3 Model parameters (AK) determined from powerful Singular Value Decomposition and additional optimizing proprietary software
Problems with TAT probes (Our fixes) • Accuracy (0.3 is expected error: 2 to 3 times better) • at best, 0.6 to 0.8º accurate • large variability seen (random errors and biases) • changing calibration (birds, other factors) • Probe heater (no heater required) • largest failure mode = delay time, repair costs • limits temperature accuracy • Probe drag (far less drag) • additional fuel costs = approximately $3M per year for 8000 aircraft in USA • Probe’s radar cross section (far less cross section) Military already seeking flush mounted versions of TAT and pitot tube
Figure from Rosemount (BF Goodrich) Technical Report 5755, Rev B, 1990 TT = TAT TS = SAT TM = measured total temperature TR = recovery temp Possible errors: Probe heater Correction factor Slow time response Self heating (I2 R ) Extreme environment TT = TS ( 1 + 0.2 M 2 ) Extreme: long term effects of rain, snow, hail, icing can damage sensor
WVSSII Installation at United Parcel Service Maintenance Facility Photo Credit: UPS Dispatch Contact for Usage: Randy Baker/UPS; Email: email@example.com
UCAR Patented Mobile Temperature Sensor (MTS) Thermal shielding (insolating gaskets) above and below T sensor area
Atmospheric trace gases from mobile platforms
Diode lasers and quantum cascade (QC) lasers for various trace gases Air quality (regional and global pollution) and climate change QC lasers invented in 1994 these are very small lasers (smaller than diode laser) key is operation at room temperature in continuous wave (cw) mode prices are still coming down
Diode lasers or QC lasers for atmospheric trace gases Same architecture as WVSS-II -- same air sampler; 1.37 μm replaced with longer wavelength laser -- single path or multiple path (Herriott cell) depending on species -- internal Systems Electronic Box (SEB) about same size -- higher price than WVSS-II (function of laser costs) Initial products design for CO2 and O3 [α = 1 x 10-4 accuracy = 5%] Feature ozone (9.2 μm) Carbon dioxide (2.7 μm) minimum detectable signal 0.01 ppmv 0.1 to 0.5 ppmv maximum detectable signal 10 ppmv 1000 ppmv path length (in centimeters) 600 24 measured precision 2% or 0.01 ppmv 1% or 0.1 to 0.5 ppmv
What is driving the need for more accuracy? An evolving, complex, global society – where all inhabitants are striving to raise their standard of living
“Accurate” Atmospheric Monitoring Data will escalate in value over time • Weather and climate already impact about 1/7 of a 7 trillion dollar USA economy • Consider growth in 7 major socioeconomic areas • Energy: largest single issue for USA and world (see charts) • Water: second largest issue for society (see chart) • Food: not as serious as before (see chart) • Transportation: major growth area (see chart) • Weather impacts (human health, safety, etc) vs 1.1% pop. growth • Climate change (global warming uncertainty vs energy conflict) • Construction: population growth 1% per year for several decades • Value of “accurate” environmental data will double approximately every 6-8 years in future.
Next Generation Air Transportation System (NGATS): Projected demand 120 million additional international passengers are expected by 2025 one billion expected in US air space by 2015 passenger demand will double or triple by 2025; cargo will triple speed and predictability of air transportation has businesses depending upon just in time air shipments for production efficiency and for keeping inventory costs low – improving our standard of living) doing nothing will cost consumers $30 billion annually Importance to United States civil aviation products and services generate a significant surplus for US trade accounts contribute to the $100 billion a year tourism from abroad air transportation has spawned a highly technical work force aviation technologies, products, and services underpin the advanced capabilities of our national defense and homeland security