ALMA: imaging at the outer limits of radio astronomy

The Atacama large mm/sub-mm array (ALMA) has antennas arrayed over baselines up to 18 km in extent which will constitute over 7000 m/sup 2/ of collecting area, enabling it to provide images of unprecedented clarity and detail. Unlike existing arrays, it will combine interferometric and single telescope data, providing a complete range of spatial scales with complete flux recovery. Six of a planned ten planned receiver bands will be built during the construction phase; eventually ALMA will cover all atmospheric windows in the spectral wavelength ranging from 7 mm to 0.3 mm. The combination of sensitivity, directivity, full UV coverage, precision calibration and the breadth of coverage, along with the extremely dry Chajnantor site at 16500 feet, will enable the creation of superb images of the celestial structures which emit mm and sub-mm photons. Equipment will continuously monitor atmospheric parameters, in particular the water vapor content along the telescopes' line of site, to permit real time correction of atmospheric perturbations to the observed wavefront. The observer will have a range of sophisticated data analysis techniques to be able to compensate for atmospheric and instrumental perturbations to the raw data.