Overview of the test activities performed on the interferometer of GOSAT / TANSO-FTS Louis Moreau, Raphaël Desbiens, James Veilleux, Dominique Duquette, Luc Levesque, Marc-Andre Soucy ABB Bomem Inc., 585 Charest E., Suite 300, Quebec City, Qc. G1K 9H4, Canada, louis.m.moreau@ca.abb.com Takahiro Kawashima, Jun Tanii NEC Toshiba Space Systems Ltd., 10 Nisshin-cho 1-chome, Fuchu, Japan Abstract: We present an overview of the tests performed on the flight unit of the modulator of TANSO-FTS for GOSAT mission. The results include tests on the interferometer module before and after integration to the sensor. OCIS Codes: (280.4991) Passive remote sensing; (300.6190) Spectrometers; 1. Introduction The Greenhouse gases Observing SATellite (GOSAT) is designed to monitor the global distribution of carbon dioxide (CO 2 ) from orbit. It is a joint project of Japan Aerospace Exploration Agency (JAXA), the Ministry of Environment (MOE), and the National Institute for Environmental Studies (NIES). JAXA is responsible for the satellite and instrument development, MOE is involved in the instrument development, and NIES is responsible for the satellite data retrieval. The objectives of GOSAT are to monitor the column density of greenhouse gases, especially CO 2 and CH 4 , worldwide; to identify sources and sinks of theses gases and to study the absorption and emission levels of greenhouse gases per continent or large country over a certain period of time [1]. TANSO-FTS (Thermal And Near infrared Sensor for carbon Observation – Fourier Transform Spectrometer) is one of the two main instruments of GOSAT. NEC Toshiba Space System (NTS), the prime contractor of the instrument subcontracted ABB Bomem Inc. to design, build and test the interferometer module. This work presents an overview of the test campaign of the interferometer before and after integration to the system. At time of redaction, GOSAT is scheduled for launch at the end of January 2009. 2. Overview of the interferometer module The TANSO-FTS is a Fourier transform spectrometer that operates from 700 cm -1 to 12900 cm -1 . The interferometer sub-system consists of tree modules: the Opto-Mechanical (OM) module and two remote control electronics modules. The OM module is inspired by the ACE-FTS interferometer launched on SCISAT-1 in August 2003, as well as by ABB’s expertise in commercial laboratory and process analyzers. It is a cube-corner interferometer based on a pendulum scan arm. The maximum optical path difference of 2.5 cm provides an unapodized spectral resolution of 0.2 cm -1 across a wide spectral range going from 750 nm to >15 µm. The TANSO interferometer accommodates an optical beam of 68 mm in diameter to provide the high throughput needed for earth observation, without use of telescope. The scan arm motion is induced by a voice coil actuator driven by a sophisticated servo-control algorithm. A metrology system built around a 1310 nm distributed feedback laser diode provides the position and speed information to the motion control algorithm. The scan speed can be adjusted for scanning periods of 1.1 s, 2 s and 4 s. The main structure of the interferometer is made of aluminum and holds the beamsplitter as well as the scanning mechanism. Since there is a mismatch in the coefficients of thermal expansion between the aluminum interferometer and the instrument optical bench, ABB has used flexure mounts to avoid possible deformations of the optics across the operating temperature range. For additional stiffness and contamination control, the interferometer is protected by a cover. With its protective cover and control electronics, the entire interferometer module weighs 22.4 kg. [2] 3. Overview of the test campaign The main tests affecting the spectro-radiometric performance that were performed on the interferometer prior to delivery to NTS and integration within the complete instrument are: • Measurement of the optical path difference • Measurement of modulation efficiency over the operational and survival temperature range. • Measurement of the scan speed stability. • Measurement of the amplitude and signal to noise ratio of the metrology signals