Ralph Snel

Learn More
The ALMA North American and European prototype antennas have been evaluated by a variety of measurement systems to quantify the major performance specifications. Nearfield holography was used to set the reflector surfaces to 17 µm RMS. Pointing and fast switching performance was determined with an optical telescope and by millimeter wavelength radiometry,(More)
The GDAQI project addresses GOME in-orbit level 1 calibration issues including air-vacuum changes (UV parabola) after launch, instrument performance degradation with time, instrument polarization sensitivity (and its changes with time), etalon spectral modulation and dichroic mirror out gassing (Fig.1). New data analysis diagnostics have been developed(More)
The specific conditions of catalyst pretreatment are known to determine the properties of iron-based Fischer-Tropsch catalysts to a large extent. The phenomenon has been investigated and it was found that the extent of reduction of the surface has a major influence on the catalytic activity and selectivity. Methane is formed as the main product on those(More)
— The Atacama Large Millimeter Array (ALMA) will consist of up to 64 state-of-the-art sub-mm telescopes, subject to stringent performance specifications which will push the boundaries of the technology, and makes testing of antenna performance a likewise challenging task. Two antenna prototypes were evaluated at the ALMA Test Facility at the Very Large(More)
A comparison is made between some conventional and new methods for detecting stars in crowded stellar images. The new methods are (1) Lucy-Richardson deconvolution of the image before detection, and (2) fitting the Point Spread Function to each pixel in the image. These methods are applied to both a synthetic image and a real one. The deconvolution method(More)