Evolution, current capabilities, and future advances in satellite ultra-spectral IR sounding

Abstract

Infrared ultra-spectral spectrometers have brought in a new era of satellite remote atmospheric sounding capability. During the 1970's, after the implementation of the first satellite sounding instruments, it became evident that much higher vertical resolution sounding information was needed to be able to forecast life and property threatening localized severe weather. The demonstration of the ultra-spectral radiance measurement technology required to achieve higher vertical resolution began in 1985, with the aircraft flights of the High-resolution Interferometer Sounder (HIS) instrument. The development of satellite instruments designed to have a HIS-like measurement capability was initiated in the late 1980's. Today, after more than a decade of development time, the Atmospheric Infrared Sounder (AIRS) and the Infrared Atmospheric Sounding Interferometer (IASI) are now operating successfully from the Aqua and MetOp polar orbiting satellites, respectively. The successful development and ground demonstration of the Geostationary Imaging Fourier Transform Spectrometer (GIFTS), during this decade, is now paving the way toward future implementation of the ultra-spectral sounding capability on the international system of geostationary environmental satellites.

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ACPD
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Ultra-spectral
Sounding
W. L. Smith Sr. et al.
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Atmos. Chem. Phys. Discuss., 9, 6541–6569, 2009
www.atmos-chem-phys-discuss.net/9/6541/2009/
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmospheric
Chemistry
and Physics
Discussions
This discussion paper is/has been under review for the journal Atmospheric Chemistry
and Physics (ACP). Please refer to the corresponding final paper in ACP if available.
Evolution, current capabilities, and future
advances in satellite ultra-spectral IR
sounding
W. L. Smith Sr.1,2, H. Revercomb1, G. Bingham3, A. Larar4, H. Huang1, D. Zhou4,
J. Li1, X. Liu4, and S. Kireev2
1University of Wisconsin, Madison, Wisconsin, USA
2Hampton University, Hampton, Virginia, USA
3Space Dynamics laboratory, Logan, Utah, USA
4NASA Langley Research Center, Hampton, Virginia, USA
Received: 11 December 2008 – Accepted: 1 February 2009 – Published: 10 March 2009
Correspondence to: W. L. Smith Sr. (bill.l.smith@cox.net)
Published by Copernicus Publications on behalf of the European Geosciences Union.
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ACPD
9, 6541–6569, 2009
Ultra-spectral
Sounding
W. L. Smith Sr. et al.
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Abstract
Infrared ultra-spectral spectrometers have brought in a new era of satellite remote at-
mospheric sounding capability. During the 1970’s, after the implementation of the first
satellite sounding instruments, it became evident that much higher vertical resolution
sounding information was needed to be able to forecast life and property threatening
localized severe weather. The demonstration of the ultra-spectral radiance measure-
ment technology required to achieve higher vertical resolution began in 1985, with the
aircraft flights of the High-resolution Interferometer Sounder (HIS) instrument. The
development of satellite instruments designed to have a HIS-like measurement capa-
bility was initiated in the late 1980’s. Today, after more than a decade of development
time, the Atmospheric Infrared Sounder (AIRS) and the Infrared Atmospheric Sound-
ing Interferometer (IASI) are now operating successfully from the Aqua and MetOp
polar orbiting satellites, respectively. The successful development and ground demon-
stration of the Geostationary Imaging Fourier Transform Spectrometer (GIFTS), during
this decade, is now paving the way toward future implementation of the ultra-spectral
sounding capability on the international system of geostationary environmental satel-
lites.
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1 Introduction
The ultra-spectral resolution sounding spectrometer evolved from the need to obtain
much higher vertical resolution atmospheric soundings from space-based Earth radi-
ance measurements than could be obtained using lower resolution multi-spectral ra-
diometers. In particular, this evolution was driven by the need to produce a sounding
vertical resolution, which was consistent with the high horizontal and temporal reso-
lution achievable from geostationary orbit as needed for forecasting localized severe
weather. The evolution began with the development of a series of aircraft instruments
to demonstrate the higher vertical resolution sounding capability of ultra-spectral res-
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ACPD
9, 6541–6569, 2009
Ultra-spectral
Sounding
W. L. Smith Sr. et al.
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olution instruments. The first experimental space demonstration of the technique was
conducted from polar orbiting research satellites in order to obtain global atmospheric
chemistry and thermodynamic state data. The operational polar orbiting satellite im-
plementation has already been initiated with the European MetOp-A satellite and this
is soon to be followed by the US National Polar-orbiting Operational Environmental
Satellite System, NPOESS. Together, MetOp and NPOESS will better satisfy the de-
mands for global high vertical resolution sounding data as needed for improved ex-
tended range numerical weather prediction. The evolution towards the ultimate goal of
a global system of geostationary ultra-spectral sounders has progressed through the
successful ground demonstration of the GIFTS (Geostationary Imaging Fourier Trans-
form Spectrometer). Although the GIFTS awaits a space demonstration, Europe is
proceeding with the development of an operational GIFTS-like instrument to fly aboard
the METEOSAT Third Generation (MTG) of geostationary satellites.
In this paper, the evolution, current capability, and future advances in the ultra-
spectral IR sounding program are discussed. The impact of ultra-spectral IR sound-
ing measurements on atmospheric science and operational meteorology is illustrated
through the presentation of experimental results.
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2Evolution overview
As shown in Fig. 1, the evolution of ultra-spectral infrared remote sounding sys-
tems useful for obtaining high vertical resolution sounding observations began dur-
ing the mid-1980s with the first flights of the NASA ER-2 High-resolution Interferometer
Sounder (HIS) (Smith et al. 1979, 1987, and Revercomb et al., 1988). The HIS demon-
strated the Michelson interferometer technology and data processing techniques that
could be employed on future Earth orbiting geostationary and polar orbiting satellites.
The primary objective of HIS was to obtain high vertical resolution atmospheric tem-
perature and moisture profiles needed for improving regional and global scale weather
forecasts (Smith, 1991).
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3Polar satellite
The success of the HIS had a great impact on the design of the Atmospheric Infrared
Sounder (AIRS) (Chahine et al., 2006) for the Earth Observing System (EOS) Polar
Platform, eventually called the Aqua satellite. Since the HIS interferometer spectrom-
eter had several thousand independent spectral channels to provide the high vertical
resolution soundings, as a result of the very high system signal to noise that results
from using such a large number of noise independent data in the profile retrieval pro-
cess, the EOS AIRS was also specified to possess a similar number of spectral chan-
nels. Two designs were proposed, an interferometer like HIS and a large focal plane
detector linear array (∼2500 detector elements) grating spectrometer (Aumann et al.,
2003) in which each detector element corresponded to an independent spectral ele-
ment of the infrared spectrum. Because of the advanced technology (e.g., the large
focal plane detector arrays, a mechanical cooler for maintaining the detector arrays
at the required 60K operating temperature, and the high data rate detector readout
system) required for the grating approach, NASA decided to advance remote sensing
technology through the selection of this approach for the AIRS. The AIRS was suc-
cessfully launched into orbit on 2 May 2002.
Also motivated by the successful HIS experience, Japan built and successfully
launched into polar orbit, during 1997, the Interferometric Monitor for Greenhouse
gases (IMG), which provided the first space demonstration of the ultra-spectral sound-
ing capability. Europe also developed an advanced sounder for both atmospheric
chemistry, as well as meteorological applications for its operational polar orbiting
MetOp satellite. It chose an interferometer design, with a spectral coverage and resolu-
tion similar to the HIS, because it could achieve many more spectral channels (∼9000)
with higher spectral resolution than the AIRS grating instrument (∼2–10 times higher,
depending upon wavenumber, using current “state of the art” detector technology). The
Infrared Atmospheric Sounding Interferometer (IASI) (Chalon et al., 2001) was suc-
cessfully launched into polar orbit aboard the MetOp-2 satellite on 19 October 2006.
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Sounding
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The United States also chose a Michelson interferometer, based upon the University
of Wisconsin’s Interferometer Thermal Sounder (ITS) design, for its future National
Polar–orbiting Operational Environmental Satellite System (NPOESS). The NPOESS
instrument, called the Cross-track Infrared Sounder (CrIS) (Bloom, 2001), achieved a
spectral resolution, spectral coverage, and number of spectral channels similar to AIRS
but was produced with readily available detectors and a passive cooler at considerably
lower cost and in a much smaller volume than the AIRS grating spectrometer.
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4 Geostationary satellite
The original motivation for the HIS advanced sounder development was to provide a
vertical sounding resolution that was more compatible with the spatial and temporal
resolution achievable from geostationary orbit than that provided by the VISSR Atmo-
spheric Sounder (VAS) (Smith et al., 1981) filter wheel sounder being flown on GOES,
beginning with the GOES-D. The spacecraft version of the HIS was proposed to fly
on the first 3-axis stabilized geostationary satellite, GOES–I. However, NOAA felt that
combining the high spectral resolution interferometer, together with the 3-axis geo-
stationary satellite, was taking too great a risk for an operational satellite. Instead,
NOAA decided to fly a filter wheel instrument, similar to the NOAA satellite High res-
olution Infrared Sounder (HIRS) (Smith et al., 1979), which could be upgraded to a
Geostationary-High resolution Interferometer Sounder (G-HIS) (Smith et al., 1990) for
flight on GOES-N. A prototype of G-HIS was built during the early 1990s and tested
successfully in the Thermal Vacuum (T/V) chamber, but NOAA decided not to move
ahead with the program because of its increased cost and the perceived risk of flying
this new technology on an operational satellite. Instead, an ultra-spectral imaging in-
terferometer concept, made possible by the rapidly developing large area format focal
plane detector array technology, emerged from NASA’s Advanced Geostationary Stud-
ies (AGS) program. An instrument concept, called the Geostationary Imaging Fourier
Transform Spectrometer (GIFTS) (Smith et al., 2001), which promised to revolution-
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