Atmospheric Chemistry Instruments
Description
‘Atmospheric chemistry instruments’ is used
here to describe a range of different types
of instruments that use various techniques
and different parts of the electromagnetic
spectrum to undertake measurements of the
atmosphere’s composition. Each atmospheric
gas is characterised by its ‘absorption’ and
‘emission’ spectra, which describe how the
molecules respond to, or signal their
presence through the emission of, different
frequencies of radiation. Remote sensing
instruments exploit these ‘signatures’ to
provide information on atmospheric
composition, using measurements over a range
of wavelengths, between UV and microwave.
Atmospheric absorption tends to be dominated
by water vapour, carbon dioxide and ozone,
with smaller contributions from methane and
other trace gases. Relatively broadband
instruments can be used for measurements of
the dominant gases, but high-spectral
resolution sensors are needed to make
measurements of other species, since they
produce weaker signals, and these must be
discriminated from the signals from more
abundant gases.
The instruments are typically operated in
either:
— Nadir-viewing mode: looking directly down
to measure the radiation emitted or
scattered in a small solid angle centred
around a measurement point on Earth, with
resulting high-spatial resolution in the
horizontal direction, but limited vertical
resolution; or
— Limb-viewing mode: scanning of positions
beyond the horizon to observe paths through
the atmosphere at a range of altitudes –
providing high vertical resolution (a few
km) but limited horizontal resolution (tens
of km at best) and particularly useful for
studying the middle atmosphere.
Emission or absorption spectra can be
studied in limb-viewing mode. One approach –
known as occultation – uses known
astronomical bodies (such as the Sun and
stars) as well-characterised target sources,
and measures the effect of Earth’s
atmosphere on the radiation reaching the
satellite to determine atmospheric
composition.
|
|
|
|
|
|
|
Current & planned
instruments
|
|
ACE-FTS
|
|
PCW PHEOS - Atmospheric
|
|
|
|
CO Sensor
(ASCENDS)
|
SAGE-III
|
|
|
|
|
GAMI
|
SBUV/2
|
|
|
|
|
GEMS
|
SMR
|
|
|
|
|
GOME-2
|
Spectrometer (OCO-2)
|
|
|
|
|
HiRDLS
|
Spectrometer (OCO-3)
|
|
|
|
|
IASI
|
Spectrometer (TEMPO)
|
|
|
|
|
IPDA LIDAR
|
TANSO-FTS
|
|
|
|
|
IR Spectrometer (GACM)
|
TES
|
|
|
|
MAESTRO
(GACM)
|
TGSP
|
|
|
|
|
Microwave Limb Sounder (GACM)
|
UV Spectrometer (GACM)
(OCO-2)
|
|
|
|
|
MOPITT
|
UVAS
|
|
|
|
|
OMI
|
UVN
|
|
|
|
OMPS
sounder (GACM)
|
UVN (Sentinel-4)
|
|
|
|
|
OMS
|
UVNS (Sentinel-5 precursor)
(GACM)
|
|
|
|
|
OSIRIS
|
UVNS (Sentinel-5)
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Applications
The earliest atmospheric chemistry instruments
were deployed to measure the stratospheric
ozone content and help understanding of
stratospheric ozone depletion after this
phenomenon was discovered. They succeeded in
producing startling and convincing evidence of
the growth of the Antarctic ozone hole. Many
of the current and planned instruments
continue to provide more sophisticated and
accurate information on ozone chemistry in the
atmosphere, including data related to gases
and radicals that affect the ozone cycle.
Agencies are addressing the need for sustained
measurements of other key atmospheric
constituents including CO2, CO and CH4.
Research missions are also planned
periodically to allow detailed examination of
the complex details of atmospheric chemistry
and the possibility that such details might be
changing. The capability to provide a global
picture of the atmosphere, and how it is
changing on a daily, seasonal and geographical
basis, is ensuring demand for these
instruments in a wide range of applications.
These include: pollution monitoring;
climatology, including studies of the carbon
cycle and support to policy-making processes
such as the Kyoto Protocol; volcanic eruption
monitoring; and operational meteorology.
The trend towards improved measurement
resolutions and accuracies, profiling
measurements (rather than total column
measurements), and extended capability in the
upper troposphere/lower stratosphere will
further extend the value of these instruments
in the coming years for monitoring air quality
and modelling atmospheric processes.
|
|
