The Ionosphere as Signal and Noise in Radio Occultation by Zlbc3216

VIEWS: 5 PAGES: 21

									  The Ionosphere as Signal and Noise
         in Radio Occultation

         Christian Rocken, Sergey Sokolovskiy, Bill
     Schreiner, Doug Hunt, Stig Syndergard, Karl Hudnut

                                 UCAR COSMIC Project



Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
                            Radio Occultation

                             Ionosphere as signal



                             Ionosphere is noise        Qu i c k Ti m e ™ a n d a
                                                           d e c o m p re s s o r
                                                a re n e e d e d to s e e th i s p i c tu re .




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
Ionospheric Observations and Noise

                                                           TEC
                                                           EDP
                                                           SCINTILLATION
                                                           90 - 800 km and Plasmasphere

                                                              IMPERFECT
                                                              IONOSPHERIC
                  Qu i c k Ti m e ™ a n d a
                     d e c o m p re s s o r
                                                              CORRECTION
          a re n e e d e d to s e e th i s p i c tu re .




                                                              (25 - 90 km)

                                                              LOW QUALITY L2
                                                              OBSERVATONS
                                                              (< 20 km)



Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
                                                 QuickTime™ an d a
                                             TIFF (LZW) decomp resso r
                                          are need ed to see this picture.




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
Amount of COSMIC-observed Trans Ionospheric TEC Data

       Quality of abs. TEC ~2 TECU




                                                     COSMIC trans-
                                                     ionospheric radio
                                                     links for a 100-min
                                                     period, June 29,
                                                     2007


 Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
                 Current Latency of COSMIC TEC Data




                                Location of Low-Latency TEC Arcs




Most data are downloaded from Satellites < 100 m
Processing at CDAAC takes ~ 20 minutes
Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
                                                 QuickTime™ an d a
                                             TIFF (LZW) decomp resso r
                                          are need ed to see this picture.




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
   COSMIC - Ionosonde Comparison
Jan. 2008, distance < 500 km, time difference < 15 min, colors indicate ionosondes




    F0F2
    rms=0.60 MHz                                    HMF2
                                                    rms=57 km




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
                                                 QuickTime™ an d a
                                             TIFF (LZW) decomp resso r
                                          are need ed to see this picture.




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
               Scintillation Sensing with COSMIC
                         No scintillation                      Scintillation
                         S4=0.005                              S4=0.113




                                            GPS/MET SNR data

Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
                Global Scintillation Mapping with COSMIC
                               S4 Index Maximum between 100 - 800 km




                                             QuickTime™ and a
                                             GIF decompressor
                                       are neede d to see this picture.




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
Amplitude scintillations (S4 index based on 50-Hz observations)


                                                      E-Layer scintillation:
                                                      Occurs at all local times
                                                      except near sun-rise (3-7
                                                      LT), strongest near sun-
                                                      set (14-19 LT).
                                                      Most active between 20-
                                                      60 deg north and south
                                                      latitude
                                                      More pronounced in NH
                                                      than SH
                                                      Stronger S4 than F-layer
                                                      scintillation

  Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
Amplitude scintillations (S4 index based on 50-Hz observations)



F-Layer scintillation:
Occurs sunset to sunrise
(19 - 5 LT).
Most active in equatorial
region (+/- 30 degrees).
Weaker S4 than E-layer
scintillation




  Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
We estimate systematic ionospheric
     Ionospheric Calibration
error by computing the “mean of the
iono-free bending angle minus neutral
bending angle (from climatology) in
the 60-80 km height bin”.
We compare this quantity “smean” for
daytime vs. nighttime soundings.
COSMIC Days 0-120, 2007
-20 < Lat. < 20
DAY (11<LT<15) smean= -1.19 e-7 rad
NIGHT (2<LT<6) smean=-0.37e-7 rad

We can see the day vs. night iono bias change we expect that we can
monitor the change of this bias with the 11-year solar cycle.
    Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
       CHANGE OF 10.7 CM FLUX WITH SOLAR CYCLE




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
Relationship of F10.7 / Bending Bias/ Temperature


        CHANGE IN DAYTIME BENDING ANGLE BIAS IN
        6 YEARS IS ~ 0.3 microrad !


                              F10.7




                          BA Bias




  Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
    Apparent Stratospheric Temperature Change Due to
Ionosphere - Induced Bending Angle Bias of 0.3 microradians

                  HEIGHT [KM]                       TEMPERATURE ERROR
                                                         [DEG K]

                           20                              0.2


                           25                              0.4


                           30                              0.6




        But we can correct for this error and effectively
        eliminate it !
Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
               Linear Regression of BA Bias F10.7 Flux




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
      Ionospheric Correction In the Lower Troposphere




                                                    Meehan et al. 2008
Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
    Effect of Using L2 data to Different Penetration Depths




Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008
                                         Summary
   In the 2 years since launch COSMIC has generated and distributed
    over 1.3 million ionospheric profiles and TEC arcs
   COSMIC ionospheric observations are of high quality and most
    products are available within < 120 minutes of on-orbit collection,
    About 300 TEC Arcs / day are available within < 30 minutes
   COSMIC is now also generating a large amount of scintillation
    observations - available from CDAAC
   We can see a clear correlation between F10.7 parameter and RO
    bending angle bias - Ionospheric bias correction of RO climate
    products seems feasible
   We do not see any evidence that availability of L2C data in in
    lower troposphere introduces a bias - some improvement in RMS
    can be expected when we start using L2C and extend ionospheric
    correction lower

    Formosat3/COSMIC Workshop, Taipei, Oct. 1-3, 2008

								
To top