AIRS and GPS Occultation: Validation at the Tropopause and Pressure - - PowerPoint PPT Presentation

▶
airs and gps occultation validation at the tropopause and
SMART_READER_LITE
LIVE PREVIEW

AIRS and GPS Occultation: Validation at the Tropopause and Pressure - - PowerPoint PPT Presentation

Nov 22, 2022 142 likes •349 views

AIRS and GPS Occultation: Validation at the Tropopause and Pressure Retrieval Stephen Leroy (JPL) May 2, 2002 AIRS Science Team Meeting, May 2, AIRS and GPS Occultation (Leroy) 1 2002 Outline What are occultations? Characteristics and

slide-1
SLIDE 1

AIRS Science Team Meeting, May 2, 2002 1 AIRS and GPS Occultation (Leroy)

AIRS and GPS Occultation: Validation at the Tropopause and Pressure Retrieval

Stephen Leroy (JPL) May 2, 2002

slide-2
SLIDE 2

AIRS Science Team Meeting, May 2, 2002 2 AIRS and GPS Occultation (Leroy)

Outline

  • What are occultations? Characteristics and examples.
  • How can they be useful for AIRS? Validation in certain

limits.

  • Data availability. http://genesis.jpl.nasa.gov.
slide-3
SLIDE 3

AIRS Science Team Meeting, May 2, 2002 3 AIRS and GPS Occultation (Leroy)

Outline

  • What are occultations? Characteristics and examples.
  • How can they be useful for AIRS? Validation in certain

limits.

  • Data availability. http://genesis.jpl.nasa.gov.
slide-4
SLIDE 4

AIRS Science Team Meeting, May 2, 2002 4 AIRS and GPS Occultation (Leroy)

GPS Occultation Technique

  • Active microwave limb sounding
  • Two frequencies (1.2 and 1.6 GHz) to eliminate ionosphere
  • Vertical resolution ~100 m, horizontal resolution ~300 km
  • Insensitive to usual calibration errorsæclocks eliminated by

“double-differencing”

slide-5
SLIDE 5

AIRS Science Team Meeting, May 2, 2002 5 AIRS and GPS Occultation (Leroy)

GPS Occultation Technique (cont’d)

  • ~250 soundings per

day per receiver

  • Soundings are globally

random but roughly follow orbit track

  • GPS/MET (1995-7)

was proof-of-concept

  • Profiles refractivity:

N=77.6 p/T + 3.73e5 pw/T2

slide-6
SLIDE 6

AIRS Science Team Meeting, May 2, 2002 6 AIRS and GPS Occultation (Leroy)

An example occultation

slide-7
SLIDE 7

AIRS Science Team Meeting, May 2, 2002 7 AIRS and GPS Occultation (Leroy)

An example occultation (cont’d)

slide-8
SLIDE 8

AIRS Science Team Meeting, May 2, 2002 8 AIRS and GPS Occultation (Leroy)

Horizontal resolution issues

slide-9
SLIDE 9

AIRS Science Team Meeting, May 2, 2002 9 AIRS and GPS Occultation (Leroy)

Outline

  • What are occultations? Characteristics and examples.
  • How can they be useful for AIRS? Validation in certain

limits.

  • Data availability. http://genesis.jpl.nasa.gov.
slide-10
SLIDE 10

AIRS Science Team Meeting, May 2, 2002 10 AIRS and GPS Occultation (Leroy)

Predicted accuracy, polar lat’s

From Kursinski et al. (2000)

0.1 1 10 10 20 30 40 50 60

RSS thermal noise (SNR

0=5x10 5)

local multipath horiz along-track ionos night, sol max abel boundary: dH/H=5% hydrostatic boundary H

2O at 80

  • lat, 8km cor len

Temperature Error (K) Altitude (km)

slide-11
SLIDE 11

AIRS Science Team Meeting, May 2, 2002 11 AIRS and GPS Occultation (Leroy)

Predicted accuracy, equatorial lat’s

0.1 1 10 10 20 30 40 50 60

RSS thermal error (SNR0=5x104) local multipath horiz along-track horiz drift ionos day, sol max abel boundary: dH/H=5% abel boundary: 7%dalpha hydrostatic boundary H2O at 0olat, 0.5km cor len

Temperature Error (K) Altitude (km)

slide-12
SLIDE 12

AIRS Science Team Meeting, May 2, 2002 12 AIRS and GPS Occultation (Leroy)

Comparison to ECMWF profiles

slide-13
SLIDE 13

AIRS Science Team Meeting, May 2, 2002 13 AIRS and GPS Occultation (Leroy)

Comparison to ECMWF analysis

From Leroy (1997)

slide-14
SLIDE 14

AIRS Science Team Meeting, May 2, 2002 14 AIRS and GPS Occultation (Leroy)

Validation of MSU timeseries

Channel 4 5 Weight (%) 1000 Pressure (hPa) 200 hPa Channel 2LT

NCEP MSU Radio occultation

  • 90

90 Latitude 200 230 Brightness channel 4 (K)

NCEP MSU Radio occultation Uncertainty band 1-Jan-95 1-Jan-02 210 214 Brightness channel 4 (K) 267 271 MSU Brightness channel 2LT (K) 11.9 12.1 NCEP, Radio occultation Geopotential 200hPa (gkm) Time slot

Northern spring, 1995. From Schrøder et al. (2002)

slide-15
SLIDE 15

AIRS Science Team Meeting, May 2, 2002 15 AIRS and GPS Occultation (Leroy)

Outline

  • What are occultations? Characteristics and examples.
  • How can they be useful for AIRS? Validation in certain

limits.

  • Data availability. http://genesis.jpl.nasa.gov.
slide-16
SLIDE 16

AIRS Science Team Meeting, May 2, 2002 16 AIRS and GPS Occultation (Leroy)

Current and planned missions

CHAMP

Geophysikalisches Forschungszentrum (Potsdam), JPL Launched July 15, 2000 i=87º, z=454km, T=93.55mins, Tn=966 days Collecting occ’ns since April 6, 2001 genesis.jpl.nasa.gov

SAC-C

Comisión Nacional de Actividades Espaciales (Buenos Aires), JPL

Launched January 25, 2001 i=98.2º, z=702km, T=98.8mins, 10:15LT Collecting occ’ns since July 7, 2001 genesis.jpl.nasa.gov

GRACE

University of Texas, JPL, DLR Launched March 17, 2002 Two spacecraft, i=89-90º, z=300-500km Begin occ’n profiling July, 2002, 250-500

  • cc’ns/day

genesis.jpl.nasa.gov

slide-17
SLIDE 17

AIRS Science Team Meeting, May 2, 2002 17 AIRS and GPS Occultation (Leroy)

Local time coverage

slide-18
SLIDE 18

AIRS Science Team Meeting, May 2, 2002 18 AIRS and GPS Occultation (Leroy)

Possible plan for AIRS validation

  • Regular co-locations at polar latitudes
  • Episodic co-locations globally (SAC-C, GRACE)
  • Asynchronous validation – probably require many

footprints to cover horizontal extent of occultation!

  • http://genesis.jpl.nasa.gov - provides occultation data in

HDF-EOS

slide-19
SLIDE 19

AIRS Science Team Meeting, May 2, 2002 19 AIRS and GPS Occultation (Leroy)

Retrieve pressure

  • GPS’s absolute position information, when convolved with

a gravity model, provides heights of constant pressure surfaces.

  • As research, one can combine 3D AIRS data with
  • ccultation data to retrieve height information for all AIRS

footprints.