TIMMi (Topographic Ice Mapping Mission)

The TIMMi suite of instruments (Ku- and Ka-band) gained its appelation from an early foreseen application for millimeterwave interferometric systems, which is to map the differential penatratoin of snow-covered ice sheets, something that will help solve for the scatterer density and the depth of the ice.

The TIMMi instruments work at Ku-band (13.285 GHz) and Ka-band (35.75 GHz) and are capable of measuring grount topography to within meter level accuracy at range resolutions on the order of one meter. Becase the system operates from a fixed point (on top of local mountain tops), the azimuth resolution is a function of the distance from the 1 degree azimuth beamwidth antenna.

These two systems have been used for mapping the local topography and for characterizing diurnal fluctuations in the atmospheric water content. They have been used also to detect fine motions in campus buildings, most notable among them the 26 story library, which has displayed periodic motion on the order of 1 cm per ten seconds of sway.

The TIMMi antenna for both Ku- and Ka-band have been constructed from modified lengths of standard waveguide. Along one dimension, the structure is a slotted waveguid antenna; along the other dimension, the slots introduce a propagating paralllel plate mode which transitions into a flare in the elevation direction, mimicking a one dimensional horn. Shown in these images are the 35 GHz version of these antennas. An equivalent antenna, scaled in frequency, has also been constructed at 13 GHz.





TheTIMMi downconverter (35 GHz). Shown at right is a Ka-band to L-band downconversion step, followed on by an L-band ot baseband stage. Independent paths for the science data line the top and bottom of the structure, with LO distribution and voltage regulation lining the middle territory. Individual housings are provided for the Ka-band filter regions to give additional isolation between the channels.