Global Pollution Monitoring from Geostationary Orbit: Instrumental and Spectroscopic requirements

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Global Pollution Monitoring from Geostationary
Orbit Instrumental and Spectroscopic
requirements
Kelly Chance Harvard-Smithsonian Center for
Astrophysics

• Atmospheric Spectroscopy Applications 2008
• 27 August 2008

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Acknowledgments

• Collaborators
• Thomas P. Kurosu
• Harvard-Smithsonian Center for Astrophysics
• Xiong Liu
• NASA/UMBC/CfA
• The GeoTRACE Team
• Jack Fishman, Doreen Neil, James Crawford (NASA)
  David Edwards (NCAR) Kelly Chance, Thomas
  Kurosu, Xiong Liu R. Bradley Pierce (NOAA) Gary
  Foley, Rich Scheffe (EPA)?
• Support
• NASA, Smithsonian Institution
• European Developments
• Jörg Langen, Rose Munro, Heinrich Bovensmann
• (Autumn 2008 decision on Sentinel 4?)

Fishman et al., 2008
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Outline

• Introduction and motivation
• Description of current satellite instruments
• Determination of measurement requirements
• UV/vis gas concentrations
• Geophysical, spatial, and temporal requirements
• Compare with European requirements
• Scalable strawman
• Orbital considerations (not part of the strawman)
• Future work The two outstanding requirements

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Introduction and Motivation

• Target tropospheric gases
• UV/visible O3, NO2, SO2, HCHO, CHO-CHO
• Infrared CO, maybe CH4 and O3 (why maybe?)
• Plus aerosols
• The aims are
• To retrieve tropospheric gases from geostationary
  orbit at high spatial and temporal resolution.
• To integrate the results into air quality
  prediction, monitoring, and modeling, and
  climatological studies.

This follows our successful developments (since
1985, with SAO as U.S. investigator) of
SCIAMACHY, GOME-1, and GOME-2, plus participation
in OMI and OMPS. Successful retrievals have
involved development of algorithm physics coupled
with chemistry and transport modeling (in
collaboration with the Harvard Modeling Group),
and multiple-scattering radiative transfer
calculations. With several minor exceptions
(below) this development has been done and, in
most cases, made operational.
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GOME/SCIAMACHY/OMI/GOME-2/OMPS nadir
Previous experience (since 1985 at
SAO) Scientific and operational measurements of
pollutants O3, NO2, SO2, HCHO, CHO-CHO, and CO
(and BrO, OClO, IO, H2O)
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(No Transcript)
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Fitting UV/visible trace species

• Requires precise (dynamic) wavelength (and often
  slit function) calibration, Ring effect
  correction, undersampling correction, and proper
  choices of reference spectra (HITRAN!
  http//www.cfa.harvard.edu/hitran)?
• Best trace gas column fitting results (NO2, HCHO,
  CHOCHO, CO) come from directly fitting L1b
  radiances
• Best tropospheric O3 and SO2 from direct profile
  retrievals using optimal estimation
• Remaining developments
• Tuning PBL O3 from UV/vis, UV/IR combinations
  (demonstrated for the OMI/TES combination by SAO
  JPL) GOME-2 and IASI?
• Tuning direct PBL SO2 from optimal estimation (in
  progress)
• Improved laboratory spectroscopy O3
  (UV/visible/IR, vs. T), HCHO (UV/IR), SO2 (UV,
  vs. T), O2-O2 (343, 360, 380 nm), CH4 in CO 0 ? 2
  overtone region, especially P branch
• Improved solar irradiance (UV, visible, IR)

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Some GOME, SCIAMACHY, and OMI examples
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OMI HCHO Sample Observations Jan-Dec 2007
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Required Concentrations
In PBL. One of two issues needing the most work
(traceability from AQ reqs. and modeling)?
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Required Concentrations European Requirements
In PBL. One of two issues needing the most work
(traceability from AQ reqs and modeling)? AQ
requirements from CAPACITY Mission Requirements
for Sentinel 45 Generic at present (1.31015
1 ppbv in 0.5 km). Need further consideration of
actual AQ requirements and flowdown to
measurement requirements
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• Scalable Strawman
• North American Version
• Quantitatively developed from
• the measurement requirements

Geostationary Minimal Case
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Scalable Strawman North American Version
15o - 50oN, 60o - 130oW (parked at 0N,
95W)? SZAs 0 70 VZAs 57 (ESZA 76o)
Spatial resolution 1010 km2 footprints Sampling
every lt½ hour (27 min)
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Scalable Strawman A European Version
35o - 65oN, 15oW - 40oE (parked at 0N, 12.5
E)? Increasing SZAs and VZAs at higher
latitudes (challenge for spatial resolution and
S/N values)
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An alternative (not in baseline) Inclined 24
hour orbits!
Better viewing zenith angles at high
latitudes Possibility to measure same location
at different VZAs ? profile information (Thanx,
RVM!)?
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Radiative Transfer Modeling and Fitting Studies
Note cloud windows Use of Raman scattering and
of the oxygen collision complex O2 A band _at_762
nm not in baseline design, to keep it small and
simple Little Chappuis band coverage Potential
implications for PBL O3 (N.B. current NASA GEO O3
study)
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Measurement Requirements
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.
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Scalable Strawman Instrument Characteristics (1)

• Spatial Resolution and Sampling
• Latitude/longitude 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 lt ½
  hour (27 min).

• Detectors
• Rockwell HyViSi TCM8050A CMOS/Si PIN (as used
  by OCO)
• 3106 e- well depth will need several rows (or
  readouts) per spectrum to reach the necessary
  statistical noise levels.
• Complicated by brightness issues cant always
  have full wells.
• Conclusions from OCO characterization of these
  detectors must be fully understood.

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Scalable Strawman North American Version
15o - 50oN, 60o - 130oW (parked at 0N,
95W)? SZAs 0 70 VZAs 57 (ESZA 76o)
Spatial resolution 1010 km2 footprints Sampling
every lt½ hour (27 min)
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Scalable Strawman Instrument Characteristics (2)

• Spectral Characteristics
• 200 spectra on each of two 10242 arrays each
  spectrum uses four detector rows (800 total out
  of 1024).
• Channel 1 280-370 nm _at_ 0.09 nm sample, 0.36 nm
  resolution (FWHM).
• Channel 2 390-490 nm _at_ 0.1 nm sample, 0.4 nm
  resolution (FWHM) includes O2-O2 _at_ 477 nm.
• 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 arcsecond (readily
  achievable)
• Telescope size
• Size optics to fill sufficiently in 1 second (?
  1 cm2 (GOME size) ? v1.5 (GOME integration time)
  ? 35,800 km / 800 km 55 cm telescope optics).
  
• 
  More realistically .
• Spitzer points to 1 arcsecond 0th order,
  correctable to ? 0.1

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Sizing for 1010 km2 Footprint,1 Second
Integration Time
?Rad? Minimum clear-sky radiance, cross-section
weighted (phot s-1 nm-1 sr-1 cm-2)? f cm-2 px-1
photons cm-2 pixel-1 _at_ 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 f
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
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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 a 16-cm diameter
telescope _at_ 10 optical efficiency (GOME, a much
simpler instrument, is 1520 efficient in this
wavelength range). IR needs (CO, maybe O3, CH4)
must be addressed.
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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 (Spatial resolution rows vs.
  readouts could do 55 km2 on 1 chip with
  multiple readouts).
• Spatial Nyquist sampling must be carefully
  addressed.
• Questions Are latitude and longitude sampling
  necessarily the same? Is constant sampling
  necessary?
• IR Priorities 2.4 ?m CO gt 9.6 ?m O3 gt 4.7 ?m
  CO gt CH4.
• Scanning Fabry-Perot instruments may provide a
  compact IR solution (SAO and NASA LaRC have
  developments here).
• Options and extensions (near-term U.S. GEO-CAPE
  attention!)
• MODIS channels for aerosols? (TOMS AAI is
  automatic, but little else is operational.)
• 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.
• Visible (Chappuis) band to further improve PBL
  O3? (Discrete?)

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Major Tradeoffs and Questions
Everything is Debatable this is why it is a
strawman, but we must show why alternatives are
better.
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Outstanding Needs
Science Requirements (S/N, geophysical,
spatial, temporal) from sensitivity and modeling
studies (OSSEs), providing traceability for AQ
forecast improvement and other uses. Europe
too! Unless things change a lot, HCHO will
be the driver for instrument requirements. Then
address trade space. 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 and
OMPS have obtained. Instrument optical and
spectrograph design, including fully-informed
choice of detector-type, is the single most
important outstanding issue in demonstrating the
feasibility of geostationary pollution
measurements. N.B. PBL O3 instrument drivers!
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The End!
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Backup Slides
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Geostationary Minimal CaseScalable Strawman - 1
15o - 50o N, 60o - 130o W (parked at 0o N, 95o
W) Measure solar zenith angles from 0o
70o Effective solar zenith angles (ESZAs) 17.6o
76.0o
North American version!
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An alternative (not in baseline) Inclined 24
hour orbits! Better viewing zenith angles at
high latitudes Possibility to measure same
location at different VZAs ? profile
information (Thanx, RVM!)
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OMI Tropospheric NO2 (July 2005)
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GOME-1 HCHO
Fu et al., 2007 Monthly mean HCHO columns over
Asia as observed by GOME from 1996 to 2001 (left
panels) and as simulated by GEOS-Chem for 2001
(right panels). The GEOS-Chem simulation uses
the bottom-up emission inventories described in
the paper. Model results are sampled between
0900 and 1200 local time. GOME observations are
at about 1030 local time. The color scale is
capped at 2.5?1016 molecule cm-2 to emphasize
features. Peak GOME observations over Southeast
Asia in March and over North China Plain in June
are as high as 3.0?1016 molecule cm-2.
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Scalable Strawman North American Version
15o - 50oN, 60o - 130oW (parked at 0N,
95W)? SZAs 0 70 VZAs 57 (ESZA 76o)
Spatial resolution 1010 km2 footprints Sampling
every lt½ hour (27 min)