LEO-LEO Radio Occultation

Transcription

1 Istitute for Geophysics, Astrophysics, ad Meteorology / Uiversity of Graz Atmospheric Remote Sesig ad Climate System Research Group ARSCliSys o the art of uderstadig the climate system LEO-LEO Radio Occultatio Gottfried Kirchegast ARSCliSys Research Group, IGAM/UiGraz, Austria (gottfried.kirchegast@ui-graz.at, ad thaks to may people for iputs; from IGAM/UiGraz especially S. Schweitzer, M. Schwaerz, J. Fritzer, J. Ramsauer; see also refereces o slides. The mai fudig for the work is from ESA/ESTEC. OPAC-2 Add-O Tutorial Lecture LEO-LEO Radio Occultatio ; Sept. 4, 2004; Uiv. of Graz, Austria.

2 LEO-LEO Radio Occultatio outlie from GNSS-LEO occultatio (J. Wickert) to LEO-LEO occultatio: how the GNSS-LEO cocept is exteded LEO-LEO occultatio cocept summary LEO-LEO costellatio cocept example (ACE+ & orbit Tx view ) LEO-LEO data processig: chai, extesios from GNSS-LEO LEO-LEO ed-to-ed performace simulatios (example ACE+) cocludig remarks

3 GPS / Galileo L-Bad Trasmitter LEO Tx satellite (at ~800 km) X/K-Bad Trasmitter Radio Occultatio Methods from GNSS-LEO Radio Occultatio GNSS LEO / LEO Rx satellite Rx satellite (at ~650 km) X/K Bad X/K-Bad Receiver L Bad L-Bad Receiver Exploits refractio of L bad sigals betwee GPS/Galileo ad GNSS receivig satellites. Measuremets of phase delay bedig agle real refractivity temperature, pressure (> ~8 km). Humidity, temperature, pressure with a priori iformatio o temperature (< ~8 km).

4 Radio Occultatio Methods to LEO-LEO Radio Occultatio LEO Tx satellite (at ~800 km) X/K Bad X/K-Bad Trasmitter LEO Rx satellite (at ~650 km) X/K Bad X/K-Bad Receiver L Bad L-Bad Receiver Exploits refractio ad absorptio of X/K bad sigals (~0, 7, 23 GHz at water vapor absorptio lie) betwee LEO trasmittig ad receivig satellites. Measuremets of phase delay & amplitude bedig agle & trasmissio real & imagiary refractivity humidity, temperature, pressure (idepedetly above ~2 6 km).

5 LEO-LEO Radio Occultatio occultatio cocept summary Trasmitted Sigals LEO Tx X/K Bad Sigals (9.7, 7.25, 22.6 GHz) [basic figure: D. Feg, Uiv. of Arizoa, 200 (modified)] LEO Rx Received Sigals LEO-LEO Occultatio exploits absorptio & refractio of X/K-bad sigals alog limb paths providig measuremets of trasmissio ad Doppler shift leadig via absorptio, bedig agle, real ad imag. refractivity to key troposphere ad climate parameters such as temperature, humidity, ad geopotetial height. Iversio similar to GNSS-LEO, but providig T ad q idepedetly; also solved by direct iversio ad/or data assimilatio approach. [figure source: Nielse et al., DMI, 2003]

6 LEO-LEO Radio Occultatio costellatio cocept example (ACE+) Primary Cocept: 2 orbital plaes, couter-rotatig Tx vs. Rx sats 2 sats/plae, su-syc METOP-aliged (i ~ 98 ) 2 orbit altitudes (~650 & 850 km) Rx s i orbit spacig ~90 ; Tx s spacig 80 atea FOV: < 0 azimuth & steerable boresight favorable i terms of power etc. (due to su syc) Alterative Cocept: 2 orbital plaes, also couter-rotatig sats 2 sats/plae, polar icliatio (i = 90 ) 2 orbit altitudes (~650 & 850 km) Rx s i orbit spacig ~90 ; Tx s spacig 80 atea FOV: < 0 i azimuth favorable lik budget without steerable atea

7 LEO LEO-LEO Data Processig LEO Data Processig data processig chai (vs. GNSS data processig chai (vs. GNSS-LEO chai as referece) LEO chai as referece) BLUE - Best Liear Ubiased Estimator Baselie case (z Thres = 0): I case of severe turbulece for z < z Thres (z Thres about 3 to 6 km): ( ) ( ) ( ) [ ] y T y T x y y C K K C K x x mod + = + ( ) ( ) ( ) ( ) [ ] b b y T b y T x x C x y y C K C K C K x x + + = + mod

8 LEO-LEO Data Processig trasmissio retrieval, wave-optics example Example: hi-res ed-to-ed simulatios based o raob data (vertical samplig ~0 m) (raob: gold coast/ghaa, 5 N/0.5 W, 8 Ja 2002, 5:8 UTC) (zoom of left pael to 2 8 km) A A ( p) / A = τ 2( p) τ( p) = τ ( ) A2 ( p) / A p 2 l 2 [ τ ( )] rl p rg p pg dpg ( p) = A,2 ~ exp , 2 r p r p p dp,2 p L L G G WOP (more ifo see Poster Gorbuov & Kirc.) u,2( t) = u,2 exp[ τ, 2( p)] GOP u u ( t) / u ( t) / u τ 2( p) τ( p) = τ ( p),2,2 l 2,2,2 [figures: Gorbuov, IAP IGAM, 2004]

9 bedig agle <-> N real LEO-LEO Data Processig refractivity retrieval, Abelia trasforms d l( ') α ( a ) = 2a Forward relatio: dr r ( ') a dr with: r a a r =, r '( a) si γ = '( a ) α ( a) Abel iversio: '( a ) = exp π 2 2 a a a da Real refractivity N z a z r R 6 '( ) = 0 ( '( ) ), = c trasmissio <-> N imag r ' Forward relatio: Tr( a ) = exp 2 κ i dr 2 ' 2 r ( r ' ) ( r) da dl Tri ( a) κ i( z ) = Abel iversio: π dr da 2 2 = a a a a a da Imagiary refractivity c N z z 6 ''( ) = 0 i( i) 4π f κ i

10 LEO-LEO Performace Simulatios (example ACE+) occultatio evet coverage LEO-LEO 2Tx+2Rx LEO-LEO daily coverage, su-sychroous orbits 2Tx+2Rx LEO-LEO mothly coverage, su-sychroous orbits

11 LEO-LEO Performace Simulatios (example ACE+) for compariso, occultatio evet coverage GNSS-LEO 2Tx+2Rx GPS-LEO daily coverage, su-sychroous orbits 2Tx+2Rx GAL-LEO daily coverage, su-sychroous orbits

12 LEO-LEO Performace Simulatios (example ACE+) forward modelig: CIRA86aQ model atmosphere profiles Represetative climatological humidity ad temperature profiles

13 LEO-LEO Performace Simulatios (example ACE+) forward modelig: atmospheric loss Exemplary atmospheric amplitude loss at F=9.7GHz, F2=7.25GHz, F3=22.6GHz (F to F3 are the ACE+ frequecy chaels)

14 LEO-LEO Performace Simulatios (example ACE+) obs.. system modelig: SNR profiles at LEO-LEO receiver typical C/N 0 profiles at the ACE+ frequecies (67 TOA) 0 30 GHz absorptio structure

15 LEO-LEO Performace Simulatios (example ACE+) obs.. system modelig: istrumetal errors simulatio (0 Hz samplig rate) Example, total istrumetal amplitude errors at the ACE+ frequecies

16 LEO-LEO Performace Simulatios (example ACE+) ed-to to-ed retrieval performace simulatios, esemble Iput atmosphere for performace simulatio oe full day of ACE+ LEO-LEO evets T5L60 ECMWF aalysis (2 UTC aalysis of Sept. 5, 2002; backgroud shows itegrated liquid water desity) Samplig of ACE+ LEO- LEO occultatios over a full day (~230 occ. evets) Latitude bads of 30º each: low latitude, mid latitude, high latitude

17 LEO-LEO Performace Simulatios (example ACE+) retrieved atmospheric profiles accuracy, example results Retrieved humidity ad temperature profiles ad related errors (compared to requiremets) at the ACE+ frequecies mid-lat bad results; total istr. errors ad 3D clouds ad turbulece ivolved; (SNR, 67 dbhz)

18 Cocludig Remarks summary LEO-LEO status ad prospects The LEO-LEO method allows global high accuracy ad high vertical resolutio measuremets of humidity, temperature, ad pressure (full thermodyamic state) as fuctio of height; with o exteral iformatio above 2 6 km Results from performace studies, i particular, cofirm - the promised < 5 % specific humidity accuracy i most of the upper troposphere, outperformig ay curret sesor i this regio - that also i presece of clouds ad scitillatios the retrieved atmospheric profiles will meet their scietific requiremets (partly usig temp iformatio) - that the retrieved atmospheric profiles are essetially ubiased throughout the troposphere, idicatig their log-term climate value LEO-LEO is techically feasible, it works. it is set to become the ext geeratio radio occultatio system advacig GNSS-LEO More ifo: OPAC- Spriger Book Kirchegast ad Hoeg (2004); ESA reports Kirchegast et al. (2004a,b), o-lie at > Publicatios cotext