SAR interferometry at Venus for topography and change detection

AbstractSince the Magellan radar mapping of Venus in the early 1990’s, techniques of synthetic aperture radar interferometry (InSAR) have become the standard approach to mapping topography and topographic change on Earth. Here we investigate a hypothetical radar mission to Venus that exploits these new methods. We focus on a single spacecraft repeat-pass InSAR mission and investigate the radar and mission parameters that would provide both high spatial resolution topography as well as the ability to detect subtle variations in the surface. Our preferred scenario is a longer-wavelength radar (S or L-band) placed in a near-circular orbit at 600km altitude. Using longer wavelengths minimizes the required radar bandwidth and thus the amount of data that will be transmitted back to earth; it relaxes orbital control and knowledge requirements. During the first mapping cycle a global topography map would be assembled from interferograms taken from adjacent orbits. This approach is viable due to the slow rotation rate of Venus, causing the interferometric baseline between adjacent orbits to vary from only 11km at the equator to zero at the inclination latitude. To overcome baseline decorrelation at lower latitudes, the center frequency of a repeated pass will be adjusted relative to the center frequency of its reference pass. During subsequent mapping cycles, small baseline SAR acquisitions will be used to search for surface decorrelation due to lava flows. While InSAR methods are used routinely on Earth, their application to Venus could be complicated by phase distortions caused by the thick Venus atmosphere

The Maastricht FFQ: Development and validation of a comprehensive food frequency questionnaire for the Maastricht study.

The aim of this study was to develop and validate a comprehensive food frequency questionnaire (FFQ) for The Maastricht Study, a population-based prospective cohort study in Maastricht, The Netherlands. Item selection for the FFQ was based on explained variation and contribution to intake of energy and 24 nutrients. For validation, the FFQ was completed by 135 participants (25-70 y of age) of the Nutrition Questionnaires plus study. Per person, on average 2.8 (range 1-5) telephone-based 24-h dietary recalls (24HRs), two 24-h urinary samples, and one blood sample were available. Validity of 54 nutrients and 22 food groups was assessed by ranking agreement, correlation coefficients, attenuation factors, and ultimately deattenuated correlation coefficients (validity coefficients). Median correlation coefficients for energy and macronutrients, micronutrients, and food groups were 0.45, 0.36, and 0.38, respectively. Median deattenuated correlation coefficients were 0.53 for energy and macronutrients, 0.45 for micronutrients, and 0.64 for food groups, being >0.50 for 18 of 22 macronutrients, 16 of 30 micronutrients and >0.50 for 17 of 22 food groups. The FFQ underestimated protein and potassium intake compared with 24-h urinary nitrogen and potassium excretion by -18% and -2%, respectively. Correlation coefficients ranged from 0.50 and 0.55 for (fatty) fish intake and plasma eicosapentaenoic acid and docosahexaenoic acid, and from 0.26 to 0.42 between fruit and vegetable intake and plasma carotenoids. Overall, the validity of the 253-item Maastricht FFQ was satisfactory. The comprehensiveness of this FFQ make it well suited for use in The Maastricht Study and similar populations