Global Monitoring of Global Monitoring of Tropospheric Pollution Tropospheric Pollution

from Geostationary Orbitfrom Geostationary Orbit

Kelly ChanceKelly ChanceHarvard-Smithsonian Center for AstrophysicsHarvard-Smithsonian Center for Astrophysics

June 1, 2001 AGU Spring Meeting 2

Xiong LiuXiong LiuNASA/UMBCNASA/UMBC

Thomas KurosuThomas KurosuHarvard-Smithsonian Center for AstrophysicsHarvard-Smithsonian Center for Astrophysics

The GeoTRACE Team: The GeoTRACE Team: Jack Fishman, Doreen Neil, James Crawford Jack Fishman, Doreen Neil, James Crawford

(NASA); David Edwards (NCAR); Kelly Chance, (NASA); David Edwards (NCAR); Kelly Chance, Thomas Kurosu (Harvard-Smithsonian Center for Thomas Kurosu (Harvard-Smithsonian Center for

Astrophysics); Xiong Liu (NASA/UMBC); R. Bradley Astrophysics); Xiong Liu (NASA/UMBC); R. Bradley Pierce (NOAA); Gary Foley, Rich Scheffe (EPA)Pierce (NOAA); Gary Foley, Rich Scheffe (EPA)

Collaborators

June 1, 2001 AGU Spring Meeting 3

Outline

• Introduction and motivationIntroduction and motivation- NRC Decadal Survey: GeoCAPE MissionNRC Decadal Survey: GeoCAPE Mission

•Determination of measurement requirementsDetermination of measurement requirements- UV/visible gases discussed hereUV/visible gases discussed here- Gas concentrationsGas concentrations- Geophysical, spatial, and temporal Geophysical, spatial, and temporal

requirementsrequirements•Scalable strawmanScalable strawman•Future work – The two outstanding Future work – The two outstanding requirementsrequirements

June 1, 2001 AGU Spring Meeting 4

Introduction and Motivation

• Target tropospheric gases are O3, NO2, SO2, HCHO, CHO-CHO (plus CO and O3 in IR, plus aerosols, not discussed here).

• The aims are:1. To retrieve tropospheric gases from

geostationary orbit at high spatial and temporal resolution.

2. To integrate the results into air quality prediction, monitoring, and modeling, and climatological studies.

• Experience from previous satellites: Scientific Experience from previous satellites: Scientific and operational measurements of Oand operational measurements of O33, NO, NO22, SO, SO22, , HCHO, and CHOCHO (and BrO, IO, OClO, HHCHO, and CHOCHO (and BrO, IO, OClO, H22O).O).

• Requires precise (Requires precise (dynamicdynamic) wavelength ) wavelength (and often slit function) calibration, Ring (and often slit function) calibration, Ring effect correction, undersampling correction, effect correction, undersampling correction, and proper choices of reference spectra and proper choices of reference spectra ((HITRAN!HITRAN!))

• Remaining developments:Remaining developments:

1.1. Tuning PBL OTuning PBL O33 from UV/IR combination from UV/IR combination (demonstrated for the OMI/TES (demonstrated for the OMI/TES combination by SAO/UMBC + JPL)combination by SAO/UMBC + JPL)

2.2. Tuning direct GOME/SCIAMACHY PBL SOTuning direct GOME/SCIAMACHY PBL SO22 from optimal estimation (underway @ from optimal estimation (underway @ SAO/UMBC/U. Toronto)SAO/UMBC/U. Toronto)

Fitting trace species

Molecule Vertical column (cm-2)

Sensitivity Driver

O3 2.41016 ~10 ppbv in PBL; reality (profiling) more complicated

NO2 3.01015 Distinguish clean from moderately polluted scenes

SO2 1.01016 Distinguish structures for anthropogenic sources

HCHO 1.01016 Distinguish clean from moderately polluted scenes

CHOCHO 1.01015 Tracking of most urban diurnal variation

Required Concentrations*

*In PBL. Determined from our satellite measurements.

(Future: traceability from AQ requirements and modeling)

Example: OMI Tropospheric NO2 (July 2005)

Geostationary Minimal Case:Scalable Strawman - 1

15o - 50o N, 60o - 130o W (parked at 0o N, 95o W)Measure solar zenith angles from 0o – 70o

Radiative Transfer Modeling and Fitting Studies

Note cloudwindows: Use ofRaman scatteringand of the oxygencollision complex.

O2 A band

Molecule Fitting window (nm)

Vertical column (cm-2)

Slant column (cm-2)

O3 315-335 2.41016 5.01015

NO2 423-451 3.01015 1.11015

SO2 315-325 1.01016 1.51015

HCHO 325-357 1.01016 2.31015

CHOCHO 423-451 1.01015 3.71014

Measurement RequirementsTo Meet Required Concentrations

The slant column measurement requirements come from full multiple scattering calculations, including gas loading, aerosols, and the GOME-derived (Koelemeijer et al., 2003) albedo database, and assume a 1 km boundary layer height.

Scalable Strawman - 2

Lat/lon limits are ~3892 km N/S and 7815-5003 km E/W (6565 average), or about 390657 1010 km2 footprints.– Measure 400 spectra N/S in two 200-spectrum

integrations (each on two 10242 detector arrays – 1 UV and 1 visible).

– 2.5 seconds per longitude (21 s integration, 0.5 s step and flyback) total sampling every < ½ hour (27 min).

Detectors: Rockwell HyViSi TCM8050A CMOS/Si PIN– 3106 e- well depth; will need several rows (or readouts)

per spectrum to reach the necessary statistical noise levels.

– Complicated by brightness issues; can’t always have full wells.

Scalable Strawman - 3

• 200 spectra on each of two 10242 arrays; each spectrum uses 4 detector rows (800 total out of 1024).–Channel 1: 280-370 nm @ 0.09 nm sample, 0.36 nm

resolution (FWHM).–Channel 2: 390-490 nm @ 0.1 nm sample, 0.4 nm

resolution (FWHM); includes O2-O2 @ 477 nm.–Nyquist sampled: 4 samples per FWHM virtually

eliminates undersampling for a symmetric instrument transfer (slit) function [Chance et al., 2005].

• Pointing to 1 km = 1/35,800 = 6 arc second (easy).• Size optics to fill sufficiently in 1 second ( 1 cm2 (GOME

size) √1.5 (GOME integration time) 35,800 km / 800 km = 55 cm “telescope” optics). More realistically ….

Mol Rad cm-2 px-1 RMS px-1 aEff

O3 3.571012 2.51104 1.4010-3 1.28105 5.088

NO2 6.251012 4.87104 8.9910-3 3.09103 0.063

SO2 2.941012 2.06104 7.2510-3 4.76103 0.230

HCHO 5.651012 3.97104 5.5110-4 8.23105 20.76

CHOCHO 6.221012 4.85104 8.9010-3 3.16105 6.503

Sizing for 1010 km2 Footprint,1 Second Integration Time

Rad: Minimum clear-sky radiance, cross-section weighted (photonss-1 nm-1 sr-1 cm-2)

cm-2 px-1: # photons cm-2 pixel-1 @ instrument in 1 second;1010 km2 7.80 10-8 sr solid angle• RMS: Fitting RMS required for the minimum detectable amount

= 1 / required S/N px-1: # photons pixel-1 needed in 1 second to meet RMS-S/N

requirements; includes factor of 4 for 4 detectors rows per spectrum• aEff: Telescope collecting area (cm2) overall optical efficiency

Mol Rad cm-2 px-1 RMS n/4 aEff

O3 3.571012 2.51104 1.4010-3 1.28105 5.088

NO2 6.251012 4.87104 8.9910-3 3.09103 0.063

SO2 2.941012 2.06104 7.2510-3 4.76103 0.230

HCHO 5.651012 3.97104 5.5110-4 8.23105 20.76

CHOCHO 6.221012 4.85104 8.9010-3 3.16105 6.503

Sizing for 1010 km2 Footprint,1 Second Integration Time

Formaldehyde (HCHO) is the driver for almost any conceivable choice of requirements! (Unless VOCs are considered unimportant, in which case O3 would be the driver, with the above as a low estimate).20.76 cm2 is a16-cm diameter telescope @ 10% optical efficiency (GOME, a much simpler instrument, is 15 – 20% efficient in this wavelength range).

Also, IR needs (CO, O3) plus aerosols must be addressed.

Major Tradeoffs and Questions

Tradeoffs: # samples (footprint) vs. sensitivity (S/N) vs. integration time vs. geographical coverage vs. max SZA:– 55 km2 footprints in 1/2 hour with a 32 cm diameter

telescope, if the instrument is 10% efficient.Questions: Are lat and lon sampling necessarily the same? Is constant sampling necessary?Option: MODIS channels for aerosols? (TOMS absorbing aerosol index is automatic, but little else operationally.)–OMI aerosol products should be reviewed.– Should include polarization-resolved measurements;– Several such UV channels will improve PBL O3

[Hasekamp and Landgraf, 2002a,b; Jiang et al., 2003]. Everything is debatable; this is why it is a strawman, but we must show why alternatives are better.

Outstanding Needs1. Science Requirements (S/N, geophysical, spatial,

temporal) from sensitivity and modeling studies (OSSEs), providing traceability for AQ forecast improvement and other uses.– Unless things change a lot, HCHO will be the driver for

instrument requirements. Then address trade space.2. Instrument Design. Reducing “smile”, enabling multiple

readouts, increasing efficiency, optimizing ITF shape ….– GEO instrument is not just a super-OMI with CMOS/Si

detectors instead of CCDs. Minimal geostationary requirements imply scanning instead of a pushbroom and they imply getting many more spectra onto a rectangular detector than OMI has obtained.

– Instrument optical and spectrograph design is the single most important outstanding issue in demon-strating the feasibility of geostationary pollution measurements.

The End!