J. E. Murray

Modelling of the Beamsplitter Properties within the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) and Associated Effect on Instrument Calibration

A polarising far infrared spectrometer has been simulated to investigate the effect of Mylar substrates on polarisers. Procedural errors were found to the calibration in certain spectral regions. Comparisons with laboratory measurements are discussed.

Geostationary earth radiation budget

The Earth Radiation Budget (ERB), the balance between the incoming solar radiation from the sun and the outgoing reflected and scattered solar radiation and the thermal infrared emission from the Earth, provides information on the fundamental energy source of the climate system. To fulfil global coverage and sampling requirements, the ERB measurements have to be made from space. Broad-band measurements are necessary because all spectral regions in both the solar and infrared contribute to the radiative fluxes. Satellite data are used in a wide range of basic studies of the radiative forcing of the climate, such as understanding the effects of variations in trace gases, clouds and the surface. They also provide essential validation for climate models. All such measurements to date have been made from satellites in low earth orbit (LEO). There are strong diurnal variations in the radiation budget, particularly over land, in response to the diurnal variation of solar heating. Four LEO satellites could provide coverage of the diurnal cycle with a temporal resolution of 3 hours. At least hourly measurements are needed to resolve the diurnal cycle of tropical convection properly, and no practicable system of polar orbiting or other LEO satellites can deliver this. From the above, it appears that the only viable solution to the problem of diurnal sampling of the Earths radiation budget is the inclusion of suitable sensors on the geostationary satellites which would allow for an essentially perfect temporal sampling. Disadvantages include the fact that geostationary satellites are much further from the Earth than polar orbiters, which affects the instrumental design, and each one can only provide a limited coverage of the globe. The Geostationary Earth Radiation Budget instrument (GERB) is a highly accurate visible-infrared radiometer designed to make unique measurements of the outgoing shortwave and longwave components of the Earths Radiation Budget (ERB) from geostationary orbit. Such measurements have not been achieved previously, and are extremely important, because they will permit a rigorous test of our understanding of the diurnal variations in the ERB: this will enable improved operational weather monitoring and permit further important developments in climate change research. GERB will be launched on the (MSG) geostationary satellite in the year 2000. Both short-wave (0.32 - 4 micrometer) and total (0.32 - 30 micrometer) radiance measurements would be made, with longwave (4 - 30 micrometer) data obtained by subtraction. The accuracy requirements (1% short-wave and 0.5% longwave) are consistent with previous radiation budget measurements. The availability of GERB on MSG will also allow a more accurate calibration of the principal Meteosat Second Generation (MSG) operational sounding instrument, SEVIRI (Spinning, Enhanced Visible and InfraRed Imager).

Estimating Far Infrared Surface Emissivity over Greenland from the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS)

We report on efforts to obtain observationally based estimates of far-infrared surface emissivity over snow and ice. We highlight one flight from the CIRCCREX-COSMICS airborne campaign over Greenland during March 2015.

Investigations of Cirrus in the Far Infrared with the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS)

An overview of the results of recent field campaigns performed with the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) to study the radiative properties of cirrus in the far infrared spectral region is presented.

High Resolution Far-IR Radiative Spectra from the TAFTS Instrument during EAQUATE 2004

The EAQUATE campaign was a validation exercise for the AIRS satellite instrument, and involved two aircraft, the NASA Proteus and FAAM Bae-146. Early results of this campaign from the far-IR TAFTS instrument are presented.

Far infrared radiation measurements from the TAFTS instrument during EMERALD 2001

The TAFTS instrument was flown at high altitude in clear and cloudy sky conditions during the EMERALD project. Here we discuss the results including clear sky net flux profiling in the far infrared.

Scientific background for CLOUDS: a cloud and radiation monitoring satellite

CLOUDS is a project co-funded by the EC under FP-4, conducted by 12 European partners, also cooperating with NOAA/ETL. It is the mission study of a monitoring satellite to perform measurements necessary to describe cloud-radiation interaction in operational models for climate and long-term weather prediction. Complementary to missions for process study, CLOUDS addresses the monitoring aspect. As such, it has to comply with requirements of sufficiently frequent observing cycle, and operational sustainability. This prevents using active systems and leads to consider passive radiometry only, however exploiting as much as possible of the em spectrum, with more polarizations and more viewing geometries. The paper reports on the effort to demonstrate that, by these means, the main ingredients of the cloud-radiation interaction mechanism may be observed with sufficient accuracy. The optimal channels are determined. Clouds, aerosol radiation and precipitation are observed under identical geometry with in a range of the em spectrum spanning from 340 nm to 4.3 cm, i.e. over five orders of magnitudes, for a true multi- spectral approach.

Upgrading the database by Fourier transform spectrometry

Current work with the visible-UV FT spectrometer at Imperial College is directed at improving the data base for the astrophysically and analytically important transition elements, using complementary data from the IR obtained at the National Solar Observatory, starting with iron, chromium and cobalt. This paper highlights the gains and problems of FTS for this type of work.