Overview of FIRST instrument & exploration of capabilities JPL Weekly CLARREO Meeting September 04, 2007 Daniel Feldman, Caltech
Presentation Outline Motivation for studying the far infrared FIRST instrument description AIRS vs FIRST, synthetic cases clear sky AIRS vs FIRST, synthetic cases with clouds Spectra from 2 test flights of FIRST Multi instrument instrument analysis of clouds Rotational band vs H2O v3 band with clouds
The far infrared frontier Current spectrometers don t measure 15-100100 μm(fir) FIR, through H2O rotational band, contributes substantially to OLR, tropospheric cooling rates Cooling rates inferred from a suite of indirect measurements Cirrus causes tropospheric radiative heating in mid-ir, cooling in far-ir Cirrus effects different for TRP, SAW Figures from Mlynczak et al, SPIE, 2002
Remote sensing of far infrared: a frontier in spectroscopy FIRST = Far Infrared Spectroscopy of the Troposphere Developed at LaRC, Marty Mlynczak PI FTS w/ 0.6 cm 1 unapodized resolution, ±0.8 cm scan length Multilayer beamsplitter Germanium Polypropylene Optically inactive over broad spectral ranges 5 200 μm spectral range NeDT ~ 0.2 K 10 km IFOV, 10 multiplexed detectors LN 2 or liquid helium cooled Scan time: 1.4 8.5 sec
Prototype Configuration and Test Flight Pictures from http://stratocat.com.ar/fichas e/2005/fsu 20050607.htm
Mid and Far Infrared Spectra Comparison: LBLRTM
AIRS and FIRST T, H 2 O, O 3 clear sky retrievals Standard retrievals using a linear Bayesian update for clear sky cases: S hat = (K T S 1 e K + S 1 a ) 1 x 1 1 1 hat = x a + (K T S 1 e K + S 1 a )*K T S 1 e (y y hat ) 3 K/km prior T uncertainty 20 % vmr/km prior H 2 O, O 3 uncertainty Measurement covariance matrix uncorrelated T, O3 retrievals are comparable H2O FIRST retrieval results better than AIRS in UT, otherwise about same Normalized averaging kernels quickly reveal relative retrieval power
Spectra and residuals Much of the initial residual structure removed during retrieval Tsurf not retrieved here Retrieval using FIRST vs AIRS shows structure at low wavenumbers and larger residuals in H2O v3 band Upper troposphere H2O differences are revealed
Spectral Cooling Rates from AIRS and FIRST Initial Cooling Rates After AIRS A priori uncertainty After FIRST
Spectral signature of cirrus clouds: IR Cirrus cloud extinction efficiency IS a function of wavenumber Spectral variation allows for determination of optical thickness, particle size Figures from Yang et al, JGR, 2003
Spectral signature of cirrus clouds with FIRST Extra information regarding cirrus layer height and particle size
Ft. Sumner, NM Clear sky conditions Aqua overpass Test Flight 1 AQUA MODIS L2 Cloud Fraction Ft Sumner, NM Clear sky conditions Aqua overpass
Measurements and RTM comparison: Test Flight 1
Test Flight 2 AQUA MODIS L2 Cloud Fraction Ft. Sumner, NM; nearly clear sky; Aqua, Cloudsat/CALIPSO overpass
CALIPSO Images 2 channel lidar on Calipso platform Linear polarized signal Complementary to Cloudsat Minimum sensitivity: τ=0.005 Few clouds over test flight 2
FIRST and AIRS Cloud Signatures
A Train Spectra Measured, FIRST simulated
H2O v3 band vs rotational band Difference between cloud-cleared radiance and measured radiance in reveals impacts of clouds on water vapor cooling Brightness temperature differences in synthetic rotational band spectra, (derived d from CloudSat retrieval products) are not the same as in the v3 band
Conclusions FIRST provides a comprehensive description of the far infrared T, O3 retrievals comparable to AIRS Improved H2O retrieval relative to AIRS, depends on NeDT that is achieved Coolingrate informationdifference isnegligible negligible. Multi instrument analysis is powerful for understanding FIRST test flight spectra Unclear if 100 km spatial resolution spec. for CLARREO is sufficient Cloud H2O interactions fully described with rotational band measurements
Acknowledgements MartyMlynczak Mlynczak, LaRC Dave Johnson, LaRC Yuk Yung, Cl Caltech Kuo Nan Liou, UCLA Jack Margolis NASA ESSF Program