A review of RFI mitigation techniques in microwave radiometry

Radio frequency interference (RFI) is a well-known problem in microwave radiometry (MWR). Any undesired signal overlapping the MWR protected frequency bands introduces a bias in the measurements, which can corrupt the retrieved geophysical parameters. This paper presents a literature review of RFI detection and mitigation techniques for microwave radiometry from space. The reviewed techniques are divided between real aperture and aperture synthesis. A discussion and assessment of the application of RFI mitigation techniques is presented for each type of radiometer.Peer ReviewedPostprint (published version

Review of the CALIMAS Team Contributions to European Space Agency's Soil Moisture and Ocean Salinity Mission Calibration and Validation

Camps, Adriano ... et al.-- 38 pages, 22 figuresThis work summarizes the activities carried out by the SMOS (Soil Moisture and Ocean Salinity) Barcelona Expert Center (SMOS-BEC) team in conjunction with the CIALE/Universidad de Salamanca team, within the framework of the European Space Agency (ESA) CALIMAS project in preparation for the SMOS mission and during its first year of operation. Under these activities several studies were performed, ranging from Level 1 (calibration and image reconstruction) to Level 4 (land pixel disaggregation techniques, by means of data fusion with higher resolution data from optical/infrared sensors). Validation of SMOS salinity products by means of surface drifters developed ad-hoc, and soil moisture products over the REMEDHUS site (Zamora, Spain) are also presented. Results of other preparatory activities carried out to improve the performance of eventual SMOS follow-on missions are presented, including GNSS-R to infer the sea state correction needed for improved ocean salinity retrievals and land surface parameters. Results from CALIMAS show a satisfactory performance of the MIRAS instrument, the accuracy and efficiency of the algorithms implemented in the ground data processors, and explore the limits of spatial resolution of soil moisture products using data fusion, as well as the feasibility of GNSS-R techniques for sea state determination and soil moisture monitoringThis work has been performed under research grants TEC2005-06863-C02-01/TCM, ESP2005-06823-C05, ESP2007-65667-C04, AYA2008-05906-C02-01/ESP and AYA2010-22062-C05 from the Spanish Ministry of Science and Innovation, and a EURYI 2004 award from the European Science FoundationPeer Reviewe

Millimeter-wave and terahertz imaging techniques

This thesis presents the development and assessment of imaging techniques in the millimeterwave (mmW) and terahertz frequency bands. In the first part of the thesis, the development of a 94 GHz passive screener based on a total-power radiometer (TPR) with mechanical beamscanning is presented. Several images have been acquired with the TPR screener demonstrator, either in indoor and outdoor environments, serving as a testbed to acquire the know-how required to perform the research presented in the following parts of the thesis. In the second part of the thesis, a theoretical research on the performance of near-field passive screeners is described. This part stands out the tradeoff between spatial and radiometric resolutions taking into account the image distortion produced by placing the scenario in the near-field range of the radiometer array. In addition, the impact of the decorrelation effect in the image has been also studied simulating the reconstruction technique of a synthetic aperture radiometer. Guidelines to choose the proper radiometer depending on the application, the scenario, the acquisition speed and the tolerated image distortion are given in this part. In the third part of the thesis, the development of a correlation technique with optical processing applicable to millimeter-wave interferometric radiometers is described. The technique is capable of correlating wide-bandwidth signals in the optical domain with no loss of radiometric sensitivity. The theoretical development of the method as well as measurements validating the suitability to correlate radiometric signals are presented in this part. In the final part of the thesis, the frequency band of the imaging problem is increased to frequencies beyond 100 GHz, covering the THz band. In this case the research is centered in tomographic techniques that include spectral information of the samples in the reconstructed images. The tomographic algorithm can provide detection and identification of chemical compounds that present a certain spectral footprint in the THz frequency band.Postprint (published version

Restoration of multichannel microwave radiometric images

A constrained iterative image restoration method is applied to multichannel diffraction-limited imagery. This method is based on the Gerchberg-Papoulis algorithm utilizing incomplete information and partial constraints. The procedure is described using the orthogonal projection operators which project onto two prescribed subspaces iteratively. Some of its properties and limitations are also presented. The selection of appropriate constraints was emphasized in a practical application. Multichannel microwave images, each having different spatial resolution, were restored to a common highest resolution to demonstrate the effectiveness of the method. Both noise-free and noisy images were used in this investigation

Multifrequency Aperture-Synthesizing Microwave Radiometer System (MFASMR). Volume 1

Background material and a systems analysis of a multifrequency aperture - synthesizing microwave radiometer system is presented. It was found that the system does not exhibit high performance because much of the available thermal power is not used in the construction of the image and because the image that can be formed has a resolution of only ten lines. An analysis of image reconstruction is given. The system is compared with conventional aperture synthesis systems

Sun effects in 2D aperture synthesis radiometry imaging and their cancellation

The Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) is the single payload of the European Space Agency’s (ESA) Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity mission. MIRAS will be the first two-dimensional aperture synthesis radiometer for earth observation. Two-dimensional aperture synthesis radiometers can generate brightness temperature images by a Fourier synthesis process without mechanical antenna steering. To do so and have the necessary wide swath for earth observation, the array is formed by small and low directive antennas, which do not attenuate enough bright noise sources that may interfere with the measurements. This study analyzes the impact of the radio-frequency emission from the sun in the SMOS mission, reviews the basic image reconstruction algorithms, and proposes a technique to minimize sun effects.Postprint (published version

Synthetic Aperture Interferometric Imaging Using a Passive Microwave Coding Device

International audience—There has been growing interest in the use of microwave synthetic aperture radiometers since their could solve the trade-off between the image resolution and the antennas aperture size. Compared to classical techniques, SAIR (Synthetic Aperture Interferometric Radiometer) can reach a large field of view (FOV) and high imaging rate. Nevertheless, the architecture of a conventional radiometer still bulky and costly. In this paper, a passive combining technique is proposed to reduce the hardware complexity as well as the dimensional requirements of the receiving antennas. Experimental results are presented to highlight the effectiveness of the proposed technique

Selection of the key earth observation sensors and platforms focusing on applications for Polar Regions in the scope of Copernicus system 2020-2030

An optimal payload selection conducted in the frame of the H2020 ONION project (id 687490) is presented based on the ability to cover the observation needs of the Copernicus system in the time period 2020–2030. Payload selection is constrained by the variables that can be measured, the power consumption, and weight of the instrument, and the required accuracy and spatial resolution (horizontal or vertical). It involved 20 measurements with observation gaps according to the user requirements that were detected in the top 10 use cases in the scope of Copernicus space infrastructure, 9 potential applied technologies, and 39 available commercial platforms. Additional Earth Observation (EO) infrastructures are proposed to reduce measurements gaps, based on a weighting system that assigned high relevance for measurements associated to Marine for Weather Forecast over Polar Regions. This study concludes with a rank and mapping of the potential technologies and the suitable commercial platforms to cover most of the requirements of the top ten use cases, analyzing the Marine for Weather Forecast, Sea Ice Monitoring, Fishing Pressure, and Agriculture and Forestry: Hydric stress as the priority use cases.Peer ReviewedPostprint (published version