Global Measurements of Pollution from Space - The MOPITT Experiment

Global Measurements of Global Measurements of Pollution from Space - The Pollution from Space - The

MOPITT ExperimentMOPITT Experiment

James R. Drummond, Department of Physics,

University of [email protected] Tel: 416-978-4723

Institute of Environmental Physics and Remote Institute of Environmental Physics and Remote SensingSensing

University of Bremen – 23 October 2001University of Bremen – 23 October 2001

mailto:[email protected]

23 October 2001 JRD - Bremen

MOPITT Team• AGENCIES• University of Toronto• York University• University of Saskatchewan• McGill University• National Center for Atmospheric

Research (NCAR)• Oxford University• Canadian Space Agency (CSA)• Meteorological Service of Canada

(MSC)• North Carolina State University

(NCSU)• COM DEV International• Hughes-Leitz• BOMEM• SED• NSERC• NASA

• Principal Investigator– James R. Drummond

• Co-Investigators– G.P. Brasseur, Max-Plank– G.R. Davis,

Saskatchewan– J.C. Gille, NCAR– G. Mand, Toronto– J.C. McConnell, York– G.D. Peskett, Oxford, UK– H.G. Reichle, Jr., NCSU– N. Roulet, McGill– J. Wang, SPIE

http://www.atmosp.physics.utoronto.ca/mopitt/home.htmlhttp://www.eos.ucar.edu/mopitt/home.html


MOPITT

• Introduction• How it all works• How we put it together• Events of the last 600 days• Some successes (it’s working well..)



MOPITT

• MOPITT measures gas concentrations in the troposphere (0-15km)

• A very challenging region because of– Underlying surface– Heterogeneous structure– Clouds


MOPITT

• The troposphere couples to the surface and to biological processes

• Region of the atmosphere most prone to modification, natural or induced

• MOPITT is making global measurements of:– Carbon monoxide profiles– Methane column amounts


The MAPS Experiment• The MAPS instrument

on the shuttle showed some of the features of the global CO field.

• Outflow from biomass burning events can be seen in this map. Other features can be seen in other seasons.

• But… incomplete...


Tropospheric Chemistry• The lifetime of CO

(about a month) means it is moved by the dynamics

• Studies of tropospheric chemical transport

• CO is also involved in tropospheric chemistry.

• It interacts with OH and O3


The Methane Problem• Methane is a greenhouse

gas and a chemical agent.

• Most measurements of methane have been made from the ground (e.g.this picture)

• Considerable debate about the methane budget (sources/sinks) and possible climatic and anthropogenic influences


MOPITT MeasurementsParameterMeasured

COprofile

COcolumn

CH4

column

Spectral Range 4.7µm 2.4µm 2.3µm

Altitude Range(km)

0-15 - -

VerticalResolution (km)

3-4 - -

HorizontalResolution (km)

22 x 22 22 x 22 22 x 22

TemporalResolution (secs)

0.4 0.4 0.4

EstimatedPrecision

10% 10% 1%


Measurement Scenario

• MOPITT operates by sensing infra-red radiation from either:

• The surface thermal emission at 4.7µm for CO profiles

• Reflected sunlight at about 2.2-2.4µm for CO and CH4 column measurements in daylight

– The radiation is modified by absorption/emission processes in the atmosphere and these changes are detected in the MOPITT instrument using Correlation Radiometry (CR) techniques


Correlation Radiometry

• Correlation Radiometry (CR) Uses a sample of the gas of interest as a filter to separate out the required emissions from the background.

• It has been used on a number of spacecraft instruments.

• MOPITT uses two methods of CR– Pressure modulation using Pressure Modulator Cells

(PMCs)– Length modulation using Length Modulator Cells

(LMCs)


Simple CR System


• In a CR system the amount of the gas is modulated and the incoming radiation is passed through the gas cell.– Radiation is modulated at the cell

frequency if it's optical frequency coincides with that of a spectral line of the gas in the cell.

– Detection of the modulated part of the radiation is performed digitally and this is a better indicator of the spectrum of interest than the raw radiance.

– Advantages are the reduction of required dynamic range and rejection of other gaseous emission

– Disadvantage is the complexity of the resulting signal


Wavelength Regions• CO fundamental band at

4.7um – Gives information on profile– But no sensitivity at ground

• CO overtone at 2.3um– Sensitive to column– Only works in sunlight

• CH4 at 2.2um– Same as CO overtone– Quite weak


Atmospheric Spectrum

3.0

2.5

2.0

1.5

1.0

0.5

0.0

TO

A R

ad

ian

ce

(x

10-3

) [

W/(

m2 s

r c

m-1

)]

222022002180216021402120

Wavenumber (cm-1)

1.0

0.8

0.6

0.4

0.2

0.0

Tra

ns

mitta

nc

e

N2O band



MOPITT - Technology

• Uses cooled detectors

• cooled preamplifiers• cooled optics• Active cooling• Digital Signal

Processing• Length Modulators• Pressure Modulators


• LMCs are the two circular object

• LMCs are made of Ti• Windows are coated

Ge• “Gold” object is a

molecular sieve


MOPITT - Instrument


MOPITT Calibration

• MOPITT has a saw-tooth scan - takes 13 secs

• A space view is taken every 10 scans• A two-point calibration is taken every 11

minutes• A long calibration is performed monthly.


MOPITT - Scanning


MOPITT - Vertical Resolution


MOPITT - Instrument


Terra Spacecraft


Terra - Other Instruments• ASTER - ASTER - Advanced Spaceborne Thermal Emission and Reflection Advanced Spaceborne Thermal Emission and Reflection

RadiometerRadiometer – 15m resolution, 0.5-12um15m resolution, 0.5-12um– Surface ImagerSurface Imager

• MISR - MISR - Multi-angle Imaging SpectroRadiometerMulti-angle Imaging SpectroRadiometer– 9 cameras, 275m resolution 0.44 - .87um9 cameras, 275m resolution 0.44 - .87um– Multi-angle surface imagerMulti-angle surface imager

• MODIS - MODIS - Moderate Resolution Imaging SpectrometerModerate Resolution Imaging Spectrometer– 250m resolution 0.4-14.5um250m resolution 0.4-14.5um– Surface imagerSurface imager

• CERES - CERES - Clouds and the Earth’s Radiant Energy SystemClouds and the Earth’s Radiant Energy System– 10km resolution, 0.3-50um10km resolution, 0.3-50um– Global radiation budgetGlobal radiation budget


LAUNCH!!

• Failed launch attempt– December 16, 1999– Change of procedure

• Successful launch– Dec 18, 1999, 18:57GMT

(10:57PST)– 9 seconds before end of window!

• Orbit:– polar, sun synchronous, – Altitude, 705km, inclination 98.4– 10:43am desc. node

C:\Program Files\QuickTime\QuickTimePlayer.exe \work\pictures\launch\terra_launch.mov




The First Map!


Instrument Maintenance

• MOPITT is mostly self-calibrating– Thermal (longer wavelength) channels calibrate

• every 2 minutes to space• Every 11 minutes to internal (room temperature) target

– Solar (shorter wavelength) channels calibrate• Every 2 minutes to space• Every 11 minutes to internal (room temperature) target• Every few months to internal (hot – 450K) target

– Cold systems need monitoring– Gas cells need attention….


On-Orbit Gain Trend• Icing on the cold optics

leads to a change in transmission and hence a gain change

• Thermal channels– Initial rate of change 1%/21

days– 2nd de-contamination

brought gain values to within 1% of initial values

– Present rate is 1%/60 days

• Solar channels– Initial rate of change

1%/100 days– 2nd de-contamination

brought gain values to within 0.5% of initial values

– Present rate is 1%/120 days

0.94

0.95

0.96

0.97

0.98

0.99

1

1.01

Norm

alised G

ain

50 100 150 200 250 300 350

Ops day (MET-13 days)

Ch 1 Ch 3 Ch 7 Ch 2 Ch 8 Ch 4

•De-contamination criteria in the future may depend on a filter shift criteria rather than a gain change


MAPS

• Before • After


One Day of MOPITT Data


Map average global may


Map average global october


Map average NA may


Map average NA october


MOPITT – THE MOVIES - I


MOPITT – THE MOVIES - II


China Weather and China Weather and MOPITTMOPITTCO for 22CO for 22ndnd August August 20002000

-MOPITT data are not available under hurricane “BIBILIS”

- Transition from high CO to low CO visible across the front


MOPITT - Validation Strategy

• Pre-launch algorithm test and verification– Use aircraft data– Add to spectral database

• Validation of MOPITT level 1 data:– Comparison with model calculations– MOPITT airborne simulator (MOPITT-A)– MOPITT Algorithm Test Radiometer - MATR – FTIR Measurements– MODIS/MAS.

• Comparison of derived products (mainly level 2 data) with correlative measurements.– Ground-based spectroscopy– Airborne in situ measurements– ground-based in situ measurements at selected sites

•


0 61 122 183 244 305 366 427 488 549

0

100

200

CO

mix

ing

ra

tio

, p

pb

v

Days after January 1, 2000

Circles: ground-based spectrometer (column)Open Triangles: MOPITT 850hPaSolid Triangles: MOPITT, middle & upper troposphere


MOPITT Anomalies

• MOPITT has been operational at 100% since March 2000• The first event occurred on May 7th 2001 (OPS127/04:07:00)• The telemetry indicated that displacer B amplitude was

excessive– Triggered Red Limit– MOPITT to SAFE as per pre-arranged procedure– Red condition occurred for about 11 minutes before SAFE mode

• Subsequent analysis indicated that during the 11 minutes– Tip B temperature increased at a rate higher than if coolers had

been turned off– Compressors A and B increased amplitude– Tip A cooled down


MOPITT OPTICS

Cooler B

Cooler A


MOPITT Anomalies

• July 5th onwards• MOPITT in SCIENCE mode• Operating normally on channels 5-8 only• Channels 1-4 are off with detectors unpowered and tip

at slightly above room temperature.• Long calibration was initiated to retrieve calibration

baseline• Cooler sub-system exhibiting more amplitude wander

than previously observed, but this is not impacting operations



MOPITT Anomalies

• On August 7 Chopper 3 motor drive current fell to zero– Not a flagged condition– no danger to instrument

• Subsequent investigation showed that power feed to the chopper had failed at (nearly) the same time

• Some indications of high current draw in the few seconds before failure

• No indication in previous telemetry of any problem• Symptoms are exactly the same as for an unverified

fuse failure pre-launch


MOPITT Anomalies

• Channels 5 and 6 are affected• Analysis of science telemetry indicates that the chopper

has failed completely open• Chopper is “loose” in the instrument

– Maneuvers in the roll direction are the most likely to cause the chopper to close

• Algorithms are being developed to utilise Channel 5 and Channel 6 data without the chopper closed information

• Initial indications are that this might be successful• Space view is being used as a substitute for the chopper

closed• Some instrument optimisation results in improved signals



Current Status

• 14 months of fully operational instrument• Data are being successfully processed for full

instrument and in current restricted mode• Data are now available at Langley DAAC• Validation is underway• There is still a lot of work to do….• There is some discussion of a MOPITT follow-

on

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Global Measurements of Pollution from Space - The MOPITT Experiment