geo-cape workshop 18-20 aug 08 a geo venture class ...€¦ · slide9 spectrometer objective ir...

GEO-CAPE Workshop 18-20 Aug 08

A GEO Venture Class tropospheric O3 and HCHO measurement concept based on

the TIMSJack Kumer, Roche, A. E.; Rairden, R.L.; and J.L. Mergenthaler, with Lockheed Martin Adv. Tech. Center

and R.B. Chatfield with NASA Ames Res. Center

The USA National Research Council Decadal Survey (NRCDS) Report for Earth Science : –describes requirements for improved atmospheric measurements to gain crucial understanding for air quality, climate change, and weather.

–We are developing compact multi-channel grating mapping spectrometers (GMS) to meet this challenge.

In this presentation we will describe:–measurements of atmospheric spectra that we have made with a proto-type GMS with λ/∆λ = 6000 in the

midwave infrared region. [we refer to the projected space application of this GMS as “TIMS”]–a potential application in a pathfinder mission for the NRCDS Geostationary Coastal and Air Pollution Events

(GEO-CAPE) Mission. It would provide:–measurements of column O3 and HCHO on the Continental USA (CONUS) with

• hourly refresh and on contiguous double sampled 5 km north-south by 10 km west-east footprints–Input to the grating mapping spectrometer would be provided by a

• front end consisting of a scan mirror and telescope with 4.5 cm aperture• The scan mirror would west to east pushbroom the slit on a CONUS wide swath in 5 km steps • Using 7s per step provides full CONUS coverage with 2-hour refresh• The O3 and HCHO would be retrieved from spectra measured on two regions centered near 3.28 and

3.56 µm, respectively. Slide 1

Based on the demonstrated measurement capability of our proto-type GMS

–retrieved O3 column should have precision 1 to 2 % depending on albedo and pollution amount

• but with the added benefit of sensitivity to boundary layer (BL) O3. • In principle, when combined with the UV measurements, it could provide a measure of the

BL O3.

▪ Options other than UV include the thermal infrared bands @ 9.6 & 4.7µm

» These options are more costly than UV & this is a major consideration for the proposed pathfinder mission

» Further more it remains to judge whether these options would be as effective as the UV

–The HCHO retrieval should have precision 3 to 15 % depending on albedo and pollution amount

Figure below from P. K. Bhartia, et al,http://www.knmi.nl/omi/research/project/meetings/ostm10/presentations.html

Slide 2

http://www.knmi.nl/omi/research/project/meetings/ostm10/presentations.html

4ºx8º

Geo measurement approach & spectral regions

Conus from Geo

~ 2500 km x 5000 km

scanline

scandirection

▬ 512 pixels along the scan line & 2 pixel slit widthSmallest footprint (ELF) is 5 km NS x 10 km WE

▬ 1000 5 km steps provide complete CONUS scan in 2 hours using 7s integration per step

Below: schematic of geo deployed tropospheric infrared mapping spectrometer TIMS, and UV mapping spectrometer. A 4.5 cm aperture is required.

Plots below of S/N per sample on a 5 x 5 km footprint and the transmittance difference in units %

UV

IR

Two MirrorScanner

TelescopePrimaryMirror

TIMS & UVSpectrometersEarth

Scene

Secondary

Slide 3

0.0

0.8

1.6

2.4

3.2

2760 2780 2800 2820wave number (cm-1)

S/N

per

spe

ctra

l sam

ple

0.0

0.2

0.4

0.6

0.8

1.0

1.2

% tr

ansm

ittan

ce d

iffer

ence

high end albedo = 0.08low end albedo =0.02% transmittance difference

wavelength = 3.53 to 3.62µm

column HCOH rmss[S/N] = 17 for albedo =0.08 [potential precision = 4.8 %]

and rmss[S/N]~6 for albedo =0.02 [potential precision = 16.7 %]

0

5

10

15

20

3035 3040 3045 3050 3055 3060wave number (cm-1)

S/N

per

spe

ctra

l sam

ple

0

2

4

6

% tr

ansm

ittan

ce d

iffer

ence

high end albedo = 0.08low end albedo=0.02% transmittance difference

column O3 rmss[S/N] = 88 for albedo =0.08 [potential precision = 1.1 %]

and rmss[S/N]~28 for albedo =0.02 [potential precision = 3.5 %]

wavelength = 3.27 to 3.30 µm

O3 & HCHO, the clean models are from the on line GATS browserclean & 40 ppbv surface enhanced O3

0

5

10

20 45 70 95 120O3 mixing ratio in ppbv

altit

ude

km

40 ppbv enhanced surface O3"clean" O3 profile

clean & doubled HCHO

0

5

10

0 1 2 3 4 5HCHO mixing ratio in ppbv

altit

ude

km

doubled HCHO profile"clean" HCHO profile

Slide 4

rmss[S/N] for 40 ppbv surface enhanced O3 on large aggregated footprints

rmss(S/N) "precision' rmss(S/N) "precision'0.080 20.8 4.8 10.4 9.60.020 8.2 12.2 4.1 24.4

50 x 50 km AG-footprintalbedo 25 x 25 km AG-footprint

Slide 5

0.0

2.0

4.0

3035 3040 3045 3050 3055 3060wave number (cm-1)

S/N

per

spe

ctra

l sam

ple high endalbedo = 0.08

low end albedo =0.02

surface O3 sensitivity on 50 x 50 km aggregated footprints+ 40 ppbv O3 rmss[S/N] = 20.8 for albedo =0.08 [potential precision = 4.8 %]

& rmss[S/N]=8.2 for albedo = 0.02 [potential precision = 12.2 %]


0

4

8

3035 3040 3045 3050 3055 3060wave number (cm-1)

S/N

per

spe

ctra

l sam

ple

0

1

2

3

% tr

ansm

ittan

ce d

iffer

ence

high end albedo = 0.08low end albedo =0.02% transmittance difference


and rmss[S/N]=13 for ALBEDO =0.02 [potential precision = 7.4 %]


O3 total column on double sampled 5 km x 10 km footprints in wet atmospheres & at 3.6 µm

–From above for the 3.3 µm region and for a standard atmosphere the total O3 can be retrieved at 1 to 3 % precision, depending on albedo, here we investigate

• The effects in the 3.3 µm region of tripling the atmospheric H2O content –The total O3 column precision is degraded to 3 to 7%, depending on albedo

• The total O3 column precision obtained from the data in the 3.6 µm region that is relatively insensitive to atmospheric H2O content

–This turns out to be the order 2 to 6 % precision, depending on albedo–Data simultaneously obtained in the two regions will together provide the order 1.5 to 4.6 % precision

Slide 6

Result for 3 x H2O

0.0

3.0

6.0

9.0

12.0

2760 2780 2800 2820wave number (cm-1)

S/N

per

spe

ctra

l sam

ple

0.0

1.0

2.0

3.0

4.0

% tr

ansm

ittan

ce d

iffer

ence

optimistic albedo = 0.080pessimistic albedo =0.0088% transmittance difference


and rmss[S/N]=18 for (H2O reflectance)/π =0.0088 [pot. precision = 5.8 %]


Summary and conclusionsFrom Geostationary deployment it is important to diurnally map O3 and HCHO column in the CONUS with

•footprints the order 5 to 10 km and with a two hour refreshIt is most important to sense O3 in the boundary layer

We have demonstrated a tropospheric infrared mapping spectrometer (TIMS) lab demonstration grating mapping spectrometer GMS that when operated in the reflective SWIR address these requirements and provide measurements of– O3 column the order 1.5 to 4.6 % precision on double sampled 5 km NS by 10

km WE footprints with 2 hour refresh and withS/N the order 5 to 12 % for 40 ppbv near surface enhanced O3 on 50 x 50 km footprints

– Together with O3 retrieved from UV, the two measurements can provide a measure of the BL O3

– The geo deployed TIMS would also provide HCHO measurements with precision the order 5 to 17 % and intrinsically better than in the UV

Next we discuss our laborotory demonstration (Lab Demo) grating mapping spectrometer that these performance estimated are based upon Slide 7

Lab Demo GMS description

Slide 8

LN2 Container

Grating Holder

78K Optical Bench

Input Lens

LN2-Cooled DemonstrationSpectrometer Structure

λc=4.65 µm∆ν=0.32 cm-1

22--D Array MountD Array Mount

Laboratory demonstration mapping spectrometerLaboratory demonstration mapping spectrometer

35 cm

HAWAII HAWAII HgCdTeHgCdTe1024x1024 Pixels1024x1024 Pixels18.5 18.5 µµm pitchm pitch

1.9 cm

HAWAII 4-Quadrant ChipArray at spectrometer focal plane on LN2-cooled base plate

Large Format 2-D Infrared Array

The Basic Technique

Spatial512 pixels

Spectral 1024 pixels

Spatial512 pixels

Spectral 1024 pixels

Column 1λ=4.56 µ2193. cm-1

Column 1024λ=4.73 µ2113 cm-1

Total Array; Dispersion 80 cm-1Dispersion per Pixel: .08 cm-1

1024 columns

Echelle Grating52.7g/mmBlaze Angle~ 65 degSiO2 with Al Coating7x8 cm ruled areaUsed in 7th Order 49.5 deg

IncidentRay

78KTemperature105Well Capacity (e)

~ 190Dark Current (e/s) at 78K, 0.5V Bias

<60 CDSRead Noise (e rms)

0.95 µShort Wave Cuton

Long Wave cutoff

~60%QE (78K)

18.5 µPixel Pitch

1024x1024Format





5.1µm Long Wave cutoff

~60%QE (78K)

18.5 µPixel Pitch

1024x1024Format

HAWAII HgCdTe MBE Array

FPA

Column 1λ=4.56 µ2193. cm-1

Column 1024λ=4.73 µ2113 cm-1

Total Array; Dispersion 80 cm-1Dispersion per Pixel: .08 cm-1

1024 columns

Echelle Grating52.7g/mmBlaze Angle~ 65 degSiO2 with Al Coating7x8 cm ruled areaUsed in 7th Order 49.5 deg

IncidentRay





Long Wave cutoff

~60%QE (78K)

18.5 µPixel Pitch

1024x1024Format





5.1µm Long Wave cutoff

~60%QE (78K)

18.5 µPixel Pitch

1024x1024Format

HAWAII HgCdTe MBE Array

FPA

5.00 CM

3.81cm

Eff Focal Length11.43 cmf/no=3

Grating

Array

LittrowOpticsDewar Window

Objective Lens

78K Enclosure

Filter

9° Along Slit

0.003° Slit width

Field of View

Laboratory demonstration grating mapping spectrometer (GMS) Optical schematic

slit

Lab Demo GMS test setup

Slide9

SpectrometerObjective

IR Source

Collimator

Laboratory Set-Up

Temperature Variable Calibration Source

slide # 1

Lab Demo GMS performance, gas cell absorption & noise

Slide 10

2112124213421442154216421742184

1 512 1024Pixel Number

Wavenumber

Spectral Calibration Using Absorption Cell DataPixel Data

Model

Spectral Calibration Using CO Absorption Cell Data-200

0

200

400

600

800

216721682169217021712172217321742175

Wavenumber

FWHM = 0.32 cm−1

[~3.7 Pix]

Assessing Spectral Line Shape Using CO absorption lines

Dispersion = 0.087 cm-1/Pix

Design Prediction: FWHM ~ 0.28 cm-1 for 60 µm Slit

Sensitivity Performance

1770

1780

1790

1800

1810

1820

1830

1840

1850

0 5 10 15 20 25Sample #

Cou

nts

Viewing 293K Blackbody

NESR(1s): 6.1x10-9 w/cm2/sr/cm-1

Extrapolated to Flight design

for single pixel

NESR 1.1x10-9

Standard Deviation: 16.9 counts ~106 Noise Electrons

Measured Responsivity: 3.6x10-10 w/cm2/sr/count

Each of the 25 sequentially observed data points is the 4 sec integratded count on a single pixel

Extrapolated to Flight design

for 36 pix aggregated footrpintl

NESR 1.8x10-10

•This observed noise performance is consistence with our noise performance modelTherefore the model can be used with confidence to extrapolate to the SWIR conceptual flight designThe S/N estimates presented above on slides 3 to 7 are based on that extrapolation of these data

Lab Demo GMS performance sky emission spectra1024 Pixels

512Pix

0 100 200 300 400 500 600 700 800 900 1000

2-Quadrant Image of Zenith SKY IR Emission Spectra

Spectra at yellow line

A First-Order Fit to the Data

2144 cm-1

2114 2124 2134 2144 2154 2164 2174 2184 2194

H20

H20H20

H20

CO COCO

N20

CO2

H20

H20

CO

2114 cm-1 2164 cm-1 2194 cm-1

Identification of atmospheric emission spectral features in the lab demo measurement range from ~ 4.56 to 4.73 µm

Slide11

Concept for geo SWIR application using the Lab Demo

3.27 to3.30 µm 3.53 to 3.62 µm

To achieve the measurements as discussed on slides 1 through 7 above the demo GMS would be used for the IR spectrometer component (slide 3)

–It would have two slits for the 3.27 – 3.30, and the 3.53 to 3.62 µm regions, respectively–These would be

•in the orders 9 and 8, respectively of the demo grating (slide 8)•directed to separated regions on the focal plane as shown schematically below

–Separate order sorting filters for each would either be mounted on the respective slits, or on the focal plane, TBD

The IIP VSWIR design is an attractive option to the Lab Demo design Separate Arrays

Dichroic Beam splitters inserted in collimatedBundle

Re Imaging Optics and Filters

Single Grating,Different orders

Band 1 Band 2

The IIP VSWIR design facilitates multiple channel measurements by utilizing • a beam spilitter in the re-imaging arm• Sorting different grating orders in each branch• A detector array per branch

Trade off advantages of the IIP design include• Utilization of entire [both arrays], rather than just ½ of HAWAII 1rg, as does the Demo based design

• Spectral resolution improved by a factor two, improved spatial resolution• Requires a factor two larger aperture, therefore S/N increases by a factor two

Trade off disadvantage of the IIP design• Increased complexity and therefore cost

The IIP VSWIR design has been demonstrated:• To the right, note the validation of calibrated VSWIR data against the Denver University FTIR data

0.E+00

1.E‐07

2.E‐07

3.E‐07

4.E‐07

5.E‐07

6.E‐07

4280 4285 4290 4295 4300

0

0.1

0.2

0.3

0.4

0.5

0.6

TIMS calibrated dataDenver U FTIR data @ 0.25 cm‐1

Slide13

estimates for emissivity near 3.3 & 3.6 um (1 of 3)

Albedo~ 0.08

Albedo~ 0.02approximate that albedo = 1- emissivity, then


Albedo~ 0.08



▪ illustrates trend to smaller albedos at larger wavelengths▪ assuming this holds on going from 4.3 to 3.3 – 3.6 um, then the large majority of the albedo in the latter region will be > 0.02, and a significant fraction will be > 0.08

Albedo~ 0.08


MAS images VIS, 2.10, 3.35 and 11.04 um

Slide17

geo-cape workshop 18-20 aug 08 a geo venture class ...€¦ · slide9 spectrometer objective ir...

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