Design and validation of a X/ Ku band feed system for ScanSAR antenna

The paper presents the design and validation of a dual band feed system for the reflector antenna of the CoReH2O (Cold Regions Hydrology High-resolution Observatory) SAR instrument, investigated under ESA contract. The antenna is a dual linearly polarized single-offset reflector, illuminated by two side feed arrays operating in X and Ku band respectively. Each array comprises seven compact multimodal horns in quasi rectangular waveguide. The horns are sequentially excited, a couple at a time, for optimum antenna pattern synthesis and secondary beams overlap. Each horn is a multiple step rectangular waveguide structure that provides the proper modal content at aperture, very close to the benchmark patterns analytically synthesized by modal superimposition at feed apertures level. The RF design has been validated through a complete characterization by test of the feeding system, proceeding from the single feeding elements to a complete feeding system composed by 4+4 elements. The measured results showed very good agreement with predictions at each stage of the campaign. Measured pattern has been used as primary source in the antenna model and very good performance have been predicted on secondary beams

Basal roughness of the Institute and Möller Ice Streams, West Antarctica: Process determination and landscape interpretation

We present a detailed analysis of bed roughness beneath Institute and Möller Ice Streams, west Antarctica, using radio-echo sounding data (RES) acquired in the austral summer of 2010/11. We assess roughness using a two-parameter approach and also assess the directionality of roughness relative to present-day ice flow. Our work highlights the wealth of additional information that resides in analyses of bed roughness. Employing these multiple approaches we show that spatially variable roughness patterns are partly a consequence of the ability of flowing ice not only to smooth the bed but also to redistribute and remove sediments, and to do this along-flow. Accordingly, we identify some fast-flow tributaries underlain by topography that has been streamlined and other tributaries that are underlain by sediments. We also identify locations that are currently protected from erosion, but where more ancient erosion may once have occurred. We conclude that detailed roughness analysis is a useful tool for landscape interpretation; and we suggest that the roughness of an ice-sheet’s bed should be viewed as the consequence not only of ancient marine sedimentation, but also as a product of more contemporary erosion and redistribution of sediments, as well as bedrock-smoothing that is ongoing because of continuing dynamic activity. In this way, basal roughness has the potential to evolve continually with ice sheet form and flow, and should not be viewed simply as a snapshot of either present-day or palaeo-basal conditions

Antenna technologies from 435 MHz to 356 GHz for ESA's candidate Earth Explorer satellite missions

\u3cp\u3eAs a result of down-selection after Phase 0 for the 7\u3csup\u3eth\u3c/sup\u3e Earth Explorer mission following the User Consultation Meeting held in Lisbon, Portugal in Jan 2009, three candidate missions were selected for further feasibility investigations (Phase A) [1]. Each of the candidate missions is now being defined in detail through two parallel and competing industrial system studies and supporting complementary science and technology studies, aiming to the final down-selection in 2012, followed by the mission implementation with a planned launch in the 2017 timeframe. The microwave payloads of those candidate missions cover the frequency range from 435 MHz to 356 GHz. The BIOMASS candidate mission aims to measure the global forest biomass at P-band (435 MHz) using the synthetic aperture radar (SAR) technique. Due to the long wavelength and large distance between the satellite and the Earth, a very large antenna aperture is required (50 - 100 m\u3csup\u3e2\u3c/sup\u3e). The CoReH\u3csub\u3e2\u3c/sub\u3eO candidate missions aims to quantitatively measure the global distribution of snow over land and sea ice at X-(9.6 GHz) and Ku-band (17.2 GHz) using the SAR technique. The PREMIER candidate mission, carrying an infrared limb sounder and a microwave limb sounder, the latter covering the frequency range of 313 - 356 GHz, aims to measure atmospheric composition in the upper Troposphere and lower Stratosphere. Three very distinct antenna technologies are required for enabling those satellite missions. This paper describes the different antenna concepts proposed and corresponding technology developments which are on-going.\u3c/p\u3