March 18, 2003 MODIS Atmosphere, St. Michaels MD Infrared Retrieval of Temperature, Moisture, Ozone, and Total Precipitable Water: Recent Update and Status

March 18, 2003 MODIS Atmosphere, St. Michaels MD

Infrared Retrieval of Temperature, Moisture, Ozone, and Total Precipitable Water: Recent Update and

Status of MOD07

Suzanne Wetzel Seemanna, Jun Lia, W. Paul Menzelb, Liam E. Gumleya, Kathleen I. Strabalaa

a Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madisonb Office of Research and Applications, NOAA/NESDIS


• Retrievals are performed in 5x5 FOV (approximately 5km resolution) clear-sky radiances over land and ocean for both day and night.

• Algorithm is a statistical synthetic regression and has the option for a subsequent nonlinear physical retrieval.

• Regression predictors include MODIS infrared radiances from bands 24, 25, 27-36 (4.4 - 14.2m).

• Clear sky determined by MODIS cloud mask (MOD35).

MODIS Atmospheric Temperature and Moisture Profiles Product, MOD07


• Overview of MOD07 products

• Brief algorithm discussion

• Evaluation of MOD07 products (Collection 3 processed after May 1, 2002)

• Recent Update (March 14, 2003)MOD07 products include:

Atmospheric precipitable water vapor (total, high, and low)Profiles of temperature and moistureTotal column ozoneStability indices (lifted index, total totals)


Hurricane Lili, 2 October 2002Terra MODIS direct broadcast

TPW (mm):

Terra MODIS total precipitable water vapor

Terra MODIS true color image


Terra MODIS Total Precipitable Water Vapor, 2 June 2001

0 6 12 18 24 30 36 42 48 54 60 66 72

TPW (mm):


PW High700-300 hPa

PW Low920 hPa - sfc

PW (mm):0 3 6 9 12 15 18


Dobson

Total Column Ozone, 2 October 2002Terra MODIS direct broadcast


Isobaric Surfaces/Profiles of Temperature13 October 2002

Terra MODIS direct broadcast

oK

Temperature

Pres

sure

(hPa

)

300 hPa

500 hPa

850 hPa


Mixing Ratio (g/kg)

Pres

sure

(hPa

)

300 hPa

500 hPa

850 hPa

Isobaric Surfaces/Profiles of Mixing Ratio13 October 2002

Terra MODIS direct broadcast


psfc psfc

I = sfc B(Tsfc) (psfc) - B(T(p)) [ d(p) / dp ] dp + (1- ) Bd

o

o

Algorithm Discussion

Clear radiance exiting the atmosphere for a MODIS IR band with wavelength :

I is measured by MODIS for = 4.4 - 14.2m (I24, I25, I27, … I36)

I can be considered a nonlinear function of the atmospheric properties including T, q, ozone, surface pressure, skin temperature, and emissivity.

We can infer a synthetic regression relationship using calculated radiances from a global set of radiosonde profiles and surface data.

Relationship is inverted to retrieve atmospheric properties from observed MODIS radiances.


Global radiosondes: NOAA-88 data set containing 7500+ global radiosonde profiles of temperature, moisture, and ozone used for training data set. 800 additional radiosondes from north African desert were added. Skin temperature and emissivity must be assigned to each profile.

RT model: Radiance calculations for each training profile are made using a 101 pressure layer transmittance model. MODIS instrument noise is added to calculated spectral band radiances.

• Radiosonde temperature-moisture-ozone profile / calculated MODIS radiance pairs are used to create the statistical regression relationship.

Bias corrections are applied to the observed MODIS radiances to account for forward model error, spectral response uncertainty, and calibration error.


Global Total Precipitable Water Comparison 22 May 2002

MODIS TPW

SSM/I f-14 TPW

Ascending and descending passes were averaged

0 6 12 18 24 30 36 42 48 54 60 66 72

TPW (mm):


TPW (mm) for 2 June 2001 over North America

MODIS Regression Retrieval MODIS Physical Retrieval GOES-8 and GOES-10

Day

Nig

ht


Comparison of TPW from MODIS (dots), GOES-8 (circles), and radiosonde (x) with SGP ARM-CART microwave radiometer

79 clear sky cases from April 2001 to October 2002

Sample of one case:

Cases were

- Manually selected by inspection ofradiance images to insure nocloud contamination. More scatter ispresent if all retrieved pixels are included.

- Rerun locally with the most recentalgorithm, except this doesn’t includethe latest bias corrections.


Mean difference MODIS - TOMS = 4.4 dobRMS = 27.4 dobmean abs % error: abs(M-T)/T = 5.9%N = 10,614

Total Ozone from MODIS (top) and TOMS (bottom)May 22, 2002

MODIS (dob)

TOM

S (d

ob)

240 260 280 300 320 340 360 380 400 420 440

240

260

2

80

30

0

320

3

40

360

380

4

00

42

0

440

Latitude (o)- 60 - 40 - 20 0 20 40 60 80- 4

0

- 20

0

20

40

6

0

80

% Error (M-T)/T


MODIS profiles agree well with radiosondes and NCEP-GDAS when the atmospheric temperature and moisture is fairly smooth and monotonic:

But not so well with smaller-scale features, such as isolated dry or moist layers:

MODISGDASSonde

Temperature

Pre

ss

ure

(h

Pa

)

Mixing Ratio Temperature

Pre

ss

ure

(h

Pa

)

Mixing Ratio

Temperature

Pre

ss

ure

(h

Pa

)

Mixing Ratio Temperature

Pre

ss

ure

(h

Pa

)

Mixing Ratio


Recent Update (delivered 14 March 2003)

Improved emissivity assigned to each training profile

Radiance bias correction update

Reduction of noise due to detector-to-detector differences and along-track noise

New retrieved skin temperature variable saved to ‘Surface_Temperature’; previously it was a copy of the ancillary GDAS surface temperature

Improved handling of surface level in integration of TPW









• Original algorithm used MODIS bands 24, 25, and 27 through 36 as predictors (4.4 - 14.2m).

• Skin temperature and emissivity in the training data set does not properly characterize desert surface conditions for the shortest wavelength bands 24 & 25 (4.4 & 4.5 m).

0 6 12 18 24 30 36 42 48 54 60 66 72

TPW (mm):

Result: Algorithm retrieved too much moisture over deserts.


New algorithm operational May 1, 2002

Instead of using the BT from bands 24 and 25 individually as predictors, we use the BT difference 4.5 minus 4.4m. This removes the surface contributions from both bands since

[sfc B(Tsfc) (psfc)]=4.5m - [

sfc B(Tsfc) (psfc)]=4.4m 0


Level 3 - TPW1 Day Global Average

Max value in 1 degree area

Images curtesy of Paul Hubanks, from MODIS web

Elevated TPW in some desert areas


Terra daytime June 2001

Aqua daytime August 2002


Original emissivity assigned to NOAA88btraining profiles: two values 0.84 and 0.95 with std 0.15, 0.03. Linear interpolation for wavelengths in between.

Measured emissivity from UCSB MODIS Land group’s Emissivity Library


Desert

Non-Desert LandIce / Snow

Seawater

Ecosystem-based Emissivity


Aqua August 24, 2002

New delivery March 14, 2003









Calculated:• NCEP-GDAS profiles of temperature and moisture (interpolated spatially) and surface pressure• MOD07 regression-based skin temperature • Representative land, ocean, ice, and desert emissivity

PFAAST forward model with HITRAN 2000 spectral database

Observed: Level 1B radiances, averaged into 5x5 FOV where all 25 pixels in the 5x5 were assigned a 95% confidence of clear or better by the MODIS cloud mask.

• Sensor zenith angle was limited to 20o. • Night only to avoid reflection in band 24 and sun glint• Ocean only to reduce uncertainty due to skin temperature and emissivity estimates.


GDAS TPWTerra 2002236

GDAS TPWAqua2002236



Aqua Terra


Aqua Terra


Aqua Terra


Aqua Terra


Aqua Terra


Terra

Aqua

19,000 cases

14,000 cases


Terra Radiance Bias at SGP-CART - Sample Individual Cases


X

X

XX

X

X

Terra Radiance Bias at SGP-CART,average of 70 cases Apr 01- Aug 02

Blue lines, calculated with approximated land emissivity

Black lines, calculated with emissivity based on AERI measurements at the SGP-CARTsite and a function of julian day(Dave Tobin).

Only significant Day/Night differenceis in Band 24


XX

Terra Radiance Bias at SGP-CART,average of 70 cases Apr 01- Aug 02

Blue lines, calculated with approximated land emissivity

Black lines, calculated with emissivity based on AERI measurements at the SGP-CARTsite and a function of julian day(Dave Tobin).

Bias of bands 29, 31, and 32 becomesnear-zero with the more accurate emissivity


Discontinuityat 50oN

Previous radiance bias corrections were latitude dependent


Global Average Radiance Bias (Observed minus Calculated) by Latitude Region+/- Standard Deviation (dotted)


New Radiance Bias Corrections, delivery v.4.1.0 (March 14 2003)

Can be a function of TPW (NCEP-GDAS) or BT.

For each band: bias slope, y-intercept, max, and min are specified.

An ancillary input ascii file for each Terra and Aqua contains this information, plus a flag specifying TPW or BT dependence.

Input files can be updated regularly without redelivery. This allows us to accommodate changes due to monthly or seasonal bias variations, instrument changes, or improvements to the radiance bias calculations (profile input, surface characterization improvements).


The Band 27 and 28 Problem

Max = 1.2 Max = 1.5









Sources of Noise in Retrieval Images:

1) Across track: Noisy or out-of-family detectors

2) Along track: Zenith angle dependent regression coefficients

Sensor Zenith

Actual MODIS sensor zenith

n-1 n n+1Zenith angleformerly usedfor retrieval


Sources of Noise in Retrieval Images:

1) Across track: Noisy or out-of-family detectors

2) Along track: Zenith angle dependent regression coefficients

Sensor Zenith

Actual MODIS sensor zenith

n-1 n n+1

New: perform two retrievals and average


Terra 2001213 0505

Collection 3 Recent Delivery


Aqua 2002288 1925

Collection 3 Recent Delivery


Future Work

• Test use of TIGR training data set instead of NOAA-88

• Improve surface characterization (emissivity, skin temperature) assigned to the training profiles

• Regression-based global radiance bias corrections

• Extend validation to other ARM CART sites, radiosondes, sun photometer network

• Applications to climate and weather studies

See next


IGBP Ecosystem

Location of TIGR3 Profiles by Ecosystem Group


Future Work

• Test use of TIGR training data set instead of NOAA-88

• Improve surface characterization (emissivity, skin temperature) assigned to the training profiles

• Regression-based global radiance bias corrections

• Extend validation to other ARM CART sites, radiosondes, sun photometer network

• Applications to climate and weather studies

See next


http://cimss.ssec.wisc.edu/modis/mod07

http://modis-atmos.gsfc.nasa.gov/

Documents

March 18, 2003 MODIS Atmosphere, St. Michaels MD Infrared Retrieval of Temperature, Moisture, Ozone, and Total Precipitable Water: Recent Update and Status