Advanced Sounder CapabilitiesAirborne Demonstration with NAST-I
W.L. Smith, D.K. Zhou, and A.M. Larar
NASA Langley Research Center, Hampton, Virginia 23681
Twelfth International TOVS Study Conference (Lorne Australia, 27 Feb-5 Mar, 2002)
NAST on Proteus
ER-2
Performance:
Ceiling 65-75 kft
Airspeed 300 ktas
Endurance 12-22 hrs
Operating Altitude: 100 to 60,000 ft
NPOESS Airborne Sounder Testbed (NAST)
IR interferometer ( NAST-I )
Spectral Range:3.5 – 16microns
Spectral Resolution:>2000 (0.25cm-1)
Spectral Coverage Comparison
NAST-I
/IASI
CrIS
AIRS/CrIS
GIFTS-SW
GIFTS-LW
GIFTS
CO2
CO
CO
N2O
N2O
CH4
CH
4
HH22O
O
H2O
H2O
N2O
N2O
CO2
CO2
O
O3
3
CO2
H2O
NAST-I Spectral Coverage Encompasses all future satellite sounders
NAST-I Observes 3-Dimensional Structure
With High Spatial Resolution and Radiometric Accuracy
p
Optimal Regression Retrieval Approach for
NAST-I Application
Ps
Ps
R = radiance
R  εBs τ s   Bd τ  (1 - ε )  Bd τ*
 = surface emissivity
Pac
Pac
Bs = surface Planck radiance
 = transmittance
S
1
s = surface transmittance
M ij    ki  kj
S k 1
* = (s)2 / 
Ps = surface pressure
nc
Pac = aircraft pressure
Ci   R j E ji
S = number of sample profiles
j1
 = radiance deviation from the mean
M = covariance matrix of 
n 1
n 1
nc
Am   K mi Ci  K mn Ps   K mi(  R j E ji )  K mn Ps E = eigenvectors of M – EOFs
i 1
i 1
j 1
C = radiance EOF amplitudes
A = {Ts, , T, q, ...} parameters
5
K and k = regression coefficients
 i   kiCi
i 1
 = emissivity EOF amplitudes
NAST-I Spectrum and Retrieval Channels
NAST-I Spm
RTVL Chnls
Retrieval Accuracy Vs EOF Number
Full Noise
1/2 Noise
10
26
58
Observed Vs Calculated from Retrieval
Retrievals for Two Different EOF #s
48 EOFs
Radiosonde
23 EOFs
Radiosonde Validation
Andros Is. Bahamas, Sept 12, 1998
Raob
NAST
3km
Distance (75 km)
Spectral H2O Sensitivity
H2O Sensitivity [dTB(,p)/dlnq(p)]
Water Vapor Retrieval Sensitivity
LW-side of H2O Band
75 km
SW-side of H2O Band
Spatial (~22km) & Temporal (~2-3hr)
Temperature Variation Over Purcell
ARM CART-Site
Sounding Validation
P
C
D
Sfc Temp (21Z)
A
B
P
Sfc Temp (19Z)
Space & Time
Variability
PROTEUS NAST-I Flight Over CART Site
Loop 1 [18:06 – 19:50 UT, March 19, 2000]
PROTEUS/NAST-I Flight Over CART Site
Loop 2 [19:50 – 21:24 UT, March 19, 2000]
VERTICAL PROFILE COMPARISONS
NOV 30
NOV 30
NOV 30
DEC 05
DEC 05
DEC 05
COMPARISON WITH GSFC-SRL (DEC. 5, 2000)
Loss of Sensitivity
NAST-I cross section is
produced by profiles from 7
high altitude passes over
Lamont OK.
GSFC-SRL Ground-based
Scanning Raman LIDAR
produced from 10 min
averages at Lamont OK
Time Average
Wallops Island Va. to Dryden Ca. (8/27/99)
Proteus NAST-I Vertical Cross-section (CLAMS 7/12/01)
16.0 UTC
13.8
14.9
This flight demonstrates the ability to observe the
spatial moisture structure below a scattered and
semi-transparent Cirrus cloud cover
Effective Surface Temperature (July 26, 2001)
GOES image
High dense convective clouds over North Carolina and
low cumulus clouds over the Delmarva peninsula
Effective Cloud Properties (July 26, 2001)
Vertical Cross-section (July 26, 2001)
Clouds
Clouds
CLOUDS
CLOUDS
CLOUDS
Clouds
IR Window Image Along Track
Surface Skin Temperature (July 14, 2001)
296.52º K ( = 0.54º K) NAST-I retrieved (within 0.1 Lat. and Lon.)
297.45º K NOAA buoy site CHLV2 measured (i.e., the bulk SST).
The cool “skin”, observed by NAST-I, relative to the sub-surface water,
observed by the buoy, is expected as a result of evaporative cooling.
Surface Emissivity (July 14, 2001)
Seawater Emissivity
Lab. measured (solid)
NAST-I retrieved (dashed)
NAST-I validation (dots)
  (R
obs
 A  A ) / ( Bs s  A )
Surface Skin
Temperature
Along Track
IR Image along track
NPOESS Aircraft Sounding Testbed (NAST) soundings over Alaska from the ~15km
flight altitude of the Proteus (March 20-21, 2001). Upper panels show flight track
and cross-section. (Note the updrafts and downdrafts seen in the water vapor at 7-9
km.) Bottom panels show comparisons with North Slope CART-site radiosondes.
March 20, 2001
March 21, 2001
Can CAT Be Measured ?
Temp
NAST Near Fairbanks AK (3/21/01; 1-2 GMT)
Moisture
Temp
Moisture
Temp
200 km
Weak Turbulence Signatures at 150 mb
Downdrafts:Warm & Dry Updrafts:Cold & Moist
Strong Turbulence Signatures at 300 mb
Moisture
Moisture
No Turbulence Signatures at 500 mb
Summary
• The NAST provides high spatial resolution radiance measurements
which can be used to validate the radiometric accuracy and retrieval
products of advanced IR sounding systems
• High spatial resolution features of atmospheric temperature, moisture,
and clouds can be retrieved from NAST radiances
• Lower tropospheric water vapor profiles depend on measurements
along the shortwave side of the 6.3 m H2O band
• High spectral/spatial resolution sounders can profile above an opaque
overcast cloud cover and above and below thin and/or broken clouds
• Surface skin temperature and emissivity can be retrieved
simultaneously from the spectral radiance measurements and this is
important for the retrieval of accurate lower tropospheric moisture
profiles
• Atmospheric turbulence might be observed with very high spatial
resolution advanced sounders