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Introduction to Measurement Techniques in Environmental Physics Summer term 2006 Postgraduate Programme in Environmental Physics University of Bremen Atmospheric Remote Sensing II Christian von Savigny. Overview – Lecture 2.
Summer term 2006
Postgraduate Programme in Environmental Physics
University of Bremen
Atmospheric Remote Sensing II
Christian von Savigny
Note: Absorption cross section typically also dependent on x
Complication: Light path dependent on
Known from measurements of solar spectrum
Absorber column amount along effective light path
Principle of wavelength pairs (online - off-line)
Org. photographic plate
Detailed description also to be found in script
Used wavelength pairs
Longest existing ozone time series
Directly transmitted solar radiation
Reflected and scattered sunlight
Scattered solar radiation
Example:Mesospheric O3 profiles retrieved from O2(1) measurements
Main source of O2(1) in dayglow: photolysis of ozone
O3 + h O2(1)JO3
O2(1) O2 + h AO2
Change in O2(1):
AO2[O2(1)]: volume emission rate, measured quantity
Steady state:[O3] = AO2[O2(1)] / JO3 retrieve [O3]
BUV (Backscatter Ultraviolet) instrument on Nimbus 4, 1970-1977
SBUV (Solar Backscatter Ultraviolet) instrument on Nimbus 7, operated from 1978 to 1990
SBUV/2 (Solar Backscatter Ultraviolet 2) instrument on the NOAA polar orbiter satellites: NOAA-11 (1989 -1994), NOAA-14 (inorbit)can measure ozone profiles as well as columns
TOMS (Total Ozone Mapping Spectrometer)first on Nimbus 7, operated from 1978 to 1993. Then three subsequent versions: Meteor 3 (1991-1994), ADEOS (1997), Earth Probe (1996-). Measures total ozone columns.
GOME (Global Ozone Monitoring Experiment)launched on ESA's ERS-2 satellite in 1995employs a nadir-viewing BUV technique that measures radiances from 240 to 793 nm. Measures O3 columns and profiles, as well as columns of NO2, H2O, SO2, BrO,OClO.
I0() spectrum at the highest tangent altitude with negligible atmospheric extinction
I(,zi) spectrum at tangent altitude zi within the atmosphere
LoS: line of sight
With kext, being the total extinction coefficient at position s along the line of sight LoS.
Extinction is usually due to Rayleigh-scattering, aerosol scattering and absorption by minor constituents:
O3 Number density
Solar occultation measurements II
Due to the different spectral characteristics of the different absorbers and scatterers the optical depth due to, e.g., O3 can be extracted.
If we assume that the cross-section does not depend on x, i.e., not on temperature and/or pressure, then
With the column density c(zi)
The measurement provides a set of column densities integrated along the line of sight for different tangent altitudes zi.
Inversion to get vertical O3 profile
Disadvantage of solar occultation measurements:
The occultation condition has to be met: Measurements only possible during orbital sunrises/sunsets
For typical Low Earth Orbits there are 14–15 orbital sunrises and sunsets per day
poor geographical coverage
SAGE (Stratospheric Aerosol and Gas Experiment) Series provided constinuous observations since 1984 to date
Latest instrument is SAGE III on a Russian Meteor-3M spacecraft
HALOE (Halogen Occultation Experiment) on UARS (Upper Atmosphere Research Satellite) operated from 1991 until end of 2005, employing IR wavelengths
POAM (Polar Ozone and Aerosol Measurement) series use UV-visible solar occultation to measure profiles of ozone, H2O, NO2, aerosols
GOMOS (Global Ozone Monitoring by Occultation of Stars) on Envisat will performs UV-visible occultation using stars
SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY) on Envisat performs solar and lunar occultation measurements providing e.g., O3, NO2, and (nighttime) NO3 profiles.
At 280 nm
Optically thin regime
Optically thick regime
Limb scatter measurements I
SME (Solar Mesosphere Explorer)launched in 1981, carried the first ever limb scatter satellite instruments. Mesospheric O3 profiles were retrieved using the Ultraviolet Spectrometer and stratospheric NO2 profiles were retrieved using the Visible Spectrometer
MSX satellite – launched in 1996 , carried a suite of UV/visiblesensors (UVISI)
SOLSE(Shuttle Ozone Limb Sounding Experiment) flown on the Space Shuttle flight in 1997. Provided good ozone profiles with high vertical resolution down to the tropopause
OSIRIS (Optical Spectrograph and Infrared Imager System) launched in 2001 on Odin satellite. Retrieval of vertical profiles of O3, NO2, OClO, BrO
SCIAMACHY (Scanning Imaging Absorption SpectroMeter for Atmospheric CHartographY), launched on Envisat in 2002. Retrieval of vertical profiles of O3, NO2, OClO, BrO and aerosols
Emission•doesn’t require sunlight •slightly less accurate than
•long time series backscatter UV
•simple retrieval technique •long horizontal path for limb obs.
•provides global maps twice
a day (good spatial coverage)
Backscatter UV•accurate • requires sunlight, so can’t be
• long time series used at night or over winter poles
• good horizontal resolution • poor vertical resolution below the
due to nadir viewing ozone peak (~30 km) due to the
effects of multiple scattering and
reduced sensitivity to the profile shape
Occultation• simple equipment • can only be made at satellite
• simple retrieval technique sunrise and sunset, which limits
• good vertical resolution number and location of meas.
• self-calibrating • long horizontal path
Limb Scattering• excellent spatial coverage • complex viewing geometry
• good vertical resolution
• data can be taken nearly • poor horizontal resolution
Example: Onion peel inversion of occultation observations
xi : O3 concentration at altitude zi
yj : O3 column density at tangent height THj
The matrix elements aij correspond to geometrical path lengths through the layers
Inverse of A exists if the determinant of A is not zero
Standard approach: least squares solution (assume N=M)
This leads to:
Add additional condition to constrain the solution, e.g.:
is a smoothing or constraint coefficient coefficient