Gillian I. Butcher

The Geostationary Earth Radiation Budget Project

This paper reports on a new satellite sensor, the Geostationary Earth Radiation Budget (GERB) experiment. GERB is designed to make the first measurements of the Earths radiation budget from geostationary orbit. Measurements at high absolute accuracy of the reflected sunlight from the Earth, and the thermal radiation emitted by the Earth are made every 15 min, with a spatial resolution at the subsatellite point of 44.6 km (north–south) by 39.3 km (east–west). With knowledge of the incoming solar constant, this gives the primary forcing and response components of the top-of-atmosphere radiation. The first GERB instrument is an instrument of opportunity on Meteosat-8, a new spin-stabilized spacecraft platform also carrying the Spinning Enhanced Visible and Infrared (SEVIRI) sensor, which is currently positioned over the equator at 3.5°W. This overview of the project includes a description of the instrument design and its preflight and in-flight calibration. An evaluation of the instrument performance after ...

The geostationary Earth radiation budget (GERB) instrument on EUMETSAT's MSG satellite

Abstract Geostationary Earth radiation budget (GERB) is an Announcement of Opportunity Instrument for EUMETSATs Meteosat Second Generation (MSG) satellite. GERB will make accurate measurements of the Earth Radiation Budget from geostationary orbit, provide an absolute reference calibration for LEO Earth radiation budget instruments and allow studies of the energetics of atmospheric processes. By operating from geostationary orbit, measurements may be made many times a day, thereby providing essentially perfect diurnal sampling of the radiation balance between reflected and emitted radiance for that area of the globe within the field of view. GERB will thus complement other instruments which operate in low orbit and give complete global coverage, but with poor and biased time resolution. GERB measures infrared radiation in two wavelength bands: 0.32–4.0 and 0.32– 30 μm , with a pixel element size of 44 km at sub-satellite point. This paper gives an overview of the project and concentrates on the design and development of the instrument and ground testing and calibration, and lessons learnt from a short time scale low-budget project. The instrument was delivered for integration on the MSG platform in April 1999 ready for the proposed launch in October 2000, which has now been delayed probably to early 2002. The ground segment is being undertaken by RAL and RMIB and produces near real-time data for meteorological applications in conjunction with the main MSG imager—SEVERI. Climate research and other applications which are being developed under a EU Framework IV pilot project will be served by fully processed data. Because of the relevance of the observations to climate change, it is planned to maintain an operating instrument in orbit for at least 3.5 years. Two further GERB instruments are being built for subsequent launches of MSG.

Performance characteristics of the PAW instrumentation on Beagle 2 (the astrobiology lander on ESA's Mars Express Mission)

The performance of the PAW instrumentation on the 60kg Beagle 2 lander for ESA’s 2003 Mars Express mission will be described. Beagle 2 will search for organic material on and below the surface of Mars in addition to a study of the inorganic chemistry and mineralogy of the landing site. The lander will utilize acquisition and preparation tools to obtain samples from below the surface, and both under and inside rocks. In situ analysis will include examination of samples with an optical microscope, Mossbauer and fluorescent X-ray spectrometers. Extracted samples will be returned to the lander for analysis, in particular a search for organics and a measurement of their isotopic composition. The PAW experiment performance data will be described along with the status of the project.

Focal plane array for the GERB instrument

The Geostationary Earth Radiation Budget (GERB) instrument is an Earth observing scientific payload launched on-board the European Space Agency Meteosat Second Generation (MSG) satellite in September 2002. The instrument measures reflected and emitted radiation in two wavebands, 0.3 - 4 μm and 4 - 30 μm. The focal plane consists of a 256-element thermoelectric linear array operating at ~300 K and four application specific integrated circuits (ASIC) providing parallel amplification, filtering and digitisation. This paper describes in detail the design, operation and performance of the GERB focal plane array.

Operation and performance of the ASIC for the GERB IR focal plane assembly

The Geostationary Earth Radiation Budget (GERB) instrument employs a 256 element thermoelectric linear array. As part of the read-out electronics, a custom ASIC has been developed which provides parallel signal processing and digitization for 64 detector pixels. Four of these ASICs combine to provide complete detector read-out, culminating in a single serial digital interface for data output. We present details of the operation and performance of the ASIC achieved as part of the GERB focal plane assembly (FPA).

Novel applications of silicon pore optics technology

In this paper we present several novel applications using X-ray mirrors based on Silicon Pore Optics technology, the present baseline technology for large effective area space based X-ray telescopes. By cutting, bending and direct bonding of mirrors cut from silicon wafers we can create a variety of structures in a number of well-defined shapes. One novel application is an X-ray half-mirror for X-ray interferometry applications based on flat, structured Si mirrors bonded to a glass support structure with a large open area ratio. A second application is to use bent silicon single crystals as a focusing Laue lens for soft gamma rays.

IR detector system for the GERB instrument

The Geostationary Earth radiation Budget (GERB) instrument will play an important role in Earth Observation Science, when it is launched on ESAs Meteosat Second Generation (MSG) satellite in 2000. The purpose of the instrument is to measure the reflected and emitted radiation of the Earth over at least a five year period, to an accuracy better than 1% within a 15 minute observation period. These scientific requirements have resulted in a detector system comprising several technological advances. The detector chosen for this instrument is a 256 pixel linear array of thermoelectric (TE) elements operating at room temperature. Based on an existing commercial design, the detector has pushed micromachined thermoelectric arrays to its limits to achieve the noise requirements. The spectral requirements of the instrument to give a flat spectral response over the 0.32 - 30 micrometer range has necessitated the blacking of the TE array. Blacking such small area arrays is a novel application and presented several problems during the course of the development. The signal conditioning electronics, consisting of 4 Application Specific Integrated Circuits, performs front end analogue signal processing, A/D conversion and multiplexing. The design of the detector system is presented in this paper, with the packaging, signal processing and blacking described in some detail.

A slatted mirror for an x-ray interferometer manufactured in silicon

A slatted mirror is a unique and crucial component in a particular design for an astronomical X-ray interferometer (Willingale 20041). The slats must be thin, < 300 μm, flat and co-planar to a very high precision. We describe the manufacture and characterisation of a prototype slatted mirror produced using a modified form of Silicon pore optics technology.

The optical demonstration of an X-ray interferometer

An X-ray interferometer can be realised using a simple geometric arrangement of flat grazing incidence mirrors and a slatted grazing incidence mirror. This optical design has the advantage that large baseline separations ~ 1m can be accomodated within an envelope 2m by 20m. Operating at 1 keV such a device could provide angular resolutions of 100 micro arc seconds with a collecting area large enough to allow imaging of many potential astronomical targets. We describe the construction of an Optical Demonstration Model, working in the visible band, used as a proof of concept for the proposed scheme.

Performance of the flight detector system for the GERB instrument

The construction and testing of the detector system for the Geostationary Earth Radiation Budget (GERB) instrument has proved to be technically challenging in a number of areas. The detector system consists of an uncooled linear array of 256 thermoelectric pixels with 4 Application Specific Integrated Circuits (ASICs) to perform front end analogue signal processing, A/D conversion and multiplexing. The design of the detector and of the ASICs represents considerable development effort to meet, in particular, requirements of low noise and broad band spectral response and the designs have been presented in previous papers. The assembly and integration of the components into a suitably packaged flight focal plane assembly (FPA) has also been challenging, requiring a solution which would allow for individual testing of components before commitment to assembly into the focal plane package. Having assembled and qualified several detector systems, the characterization and performance of the flight detector system is presented in this paper.