Instrument development.

Ground-based Folurier Transform infrared (FTIR) instruments are being produced at the University of Wisconsin (UW) and the Unliversity of Denver (UD) for the Atmospheric Radiation Measurement (ARM) Program's Cloud and Radiation Te:stbed (CART) sites as part of a joint Instrument Development Program (lOP). The three instrument types under development are summarized in Table 1 . For each ARM site, the 1 cm-1 resolution Atmospheric Emitted Radiance ilnterferometer (AERI) is expected to be operated both at the central site and at four extended boundary location~; to allow its use for radiometric studies and for remote sensing of horizontal inhomogeneities. The AERI is being built by the UW and is the primary subject of this report. The extra high resolution AERI-X and the ultra high resolution Solar Radiance Transmission Interferometer (SORTI) are planned for the central sites and are described in more ,detail in a separate abstract by the UD. The AERI will measure an accurately calibrated spectrum of the downwelling sky radiance every 10 minutes. It makes use of a commercially available interferometer (Michelson Series MB1 00 from BOMEM, Inc., of Quebec, Canada) linked to a data system of networked IBM PC computers. The major role of this lOP effort is to incorporate a subsystem for accurate radiometric calibration and to integrate the required hardware, operational control software, and analysis software into a complete system which can be linked to the CART data system and operated remotely without the attendance of expert operators.