In this work we study and demonstrate the performance of a Radio Frequency Interference detection algorithm that is applicable to fully polarized Earth Observation radiometers. The proposed Polarimetric Cross Frequency algorithm is based on analysis of spectral deviation of the 3rdand 4thStokes parameters calculated form the dual polarized input of a radiometer. We define the new algorithm, simulate its performance, compare it with other commonly used detection algorithms, and perform a demonstration with electronics that is designed against space radiometer requirements. The results of the work demonstrate that the detection performance of the proposed algorithm is better than reference algorithms in optimal conditions, however, it has weaknesses for certain signals. Therefore, in future systems our recommendation is to combine the proposed algorithm with other RFI detection algorithms.

This paper presents the simulations needed to assess the performance of the Radio Frequency Interference (RFI) processor for the Copernicus Imaging Microwave Radiometer (CIMR). A brief description of the common RFI processor used for all radiometer bands in CIMR and of the system parameters is given in sections 2 and 3, respectively. Hereafter follows a description of the simulations and how the performance can be obtained in sections 4 and 5. Conclusion is in section 6.

Radio Frequency Interference (RFI) has been an increasing problem for Earth observing radiometers - especially spaceborne - for many years as RFI adds to the power level measured by these radiometers and thereby affects the results derived from the measurements. Methods for removing RFI have been either ground processing (the only available option for older satellites like SMOS) or producing more output to improve ground processing capabilities for removing RFI as in SMAP. With the increasing demands for improved spatial and radiometric resolution the first method is insufficient and the second requires downloading too much data. During the design of the MetOp-Second Generation (MetOp-SG) satellite it has been demonstrated that on-board RFI detection is possible and for future radiometers on-board processing is the way forward. This paper introduces the RFI processor for the High Priority Copernicus Mission satellite CIMR (Copernicus Imaging Microwave Radiometer) which comprises 25 radiometer channels at five different radiometer bands.

In a traditional spaceborne microwave radiometer system with a scanning antenna, there is often a conflict between spatial and radiometric resolution. Integration over many beams per frequency might be necessary to improve radiometric resolution. Many beams may be generated using many classical feed horns or by a focal plane array (FPA) system. At C-band, horns are bulky and replacing several such horns with an FPA is an interesting option. The FPA concept uses many small antenna elements, many receivers, and powerful online digital processing. An FPA system that can replace four horns is evaluated, especially concerning power consumption.

As part of a validation of the SMOS sea ice thickness product, the DTU Space built L-band radiometer, EMIRAD-L (formerly EMIRAD 2), was participating in the MOSAiC campaign. Situated on P-deck of the German research vessel Polarstern and overlooking the sea or ice from the port side it recorded L-band radiometric data throughout the campaign. This paper briefly describes the installation, and provides some processing results as well as initial RFI findings.

ESA's Soil Moisture and Ocean Salinity (SMOS) mission was launched 2 Nov 2009 and, to date, is still in good health, providing valuable L-band observations of the Earth surface [1]. A number of products are obtained from these, including thin sea ice [2], frost/thaw soils [3], high winds [4], ocean surface wind [5] and Sun brightness temperature [6], besides the main mission measurements of soil moisture and sea surface salinity [7] [8]. This paper deals with the description and early results of some technology activities conducted by ESA applying the lessons learnt by SMOS and in preparation of an advanced L-band radiometer mission.

The Atmosphere-Space Interaction Monitor (ASIM) is an observatory mounted outside the Columbus module on the International Space Station. It has been operational since April 13th, 2018. It contains two instruments: The Modular X- and Gamma-ray Sensor (MXGS) and The Modular Multispectral Imaging Array (MMIA). The objective of ASIM is to monitor thunderstorms and auroras, including lightning discharges, especially discharges upwards above thunderstorms. This paper presents the instrument package and some first results.

For many years Radio Frequency Interference (RFI) has been an increasing problem especially for spaceborne radiometers; as a result, there has been an increasing effort on developing algorithms and hardware for counteracting RFI. Due to the amount of time it takes to develop and build spaceborne systems, this development has had a limited effect on current spaceborne systems. In spaceborne radiometer systems currently being built the need for onboard detection and blanking of RFI has been acknowledged. This paper addresses the efforts to implement RFI detection and blanking techniques on European operational spaceborne systems, MetOp Second Generation (MetOp-SG) satellites and the Copernicus High Priority Mission Passive Imaging Microwave Radiometer (CIMR) satellites.

In order to evaluate a potential calibration target for spaceborne L-band radiometer systems, a 350 × 350 km area near the Concordia station on the East Antarctica plateau was mapped by an airborne L-band radiometer. Unexpectedly, the area showed significant brightness temperature spatial variations, well correlated with bedrock topography, hence ice thickness. Using SMOS data over a poorly known part of Antarctica, ice thickness in this area has been assessed, and an existing bedrock map has been improved.

An RFI processor breadboard has been designed and developed for future spaceborne microwave radiometer systems. RFI detection is based on the anomalous amplitude, kurtosis, and cross-frequency algorithms. These are implemented in VHDL code in an FPGA. Thus algorithm performance can be assessed by proper code simulation. The breadboard has been integrated with a Ku band radiometer subjected to RFI-like signals from a laboratory generator. Simulations show that the algorithms as implemented work according to theory when subjected to pulsed sinusoidal and QPSK signals. The laboratory measurements confirm the performance for pulsed signals.

Radio Frequency Interference (RFI) is an increasing threat to proper operation of space-borne Earth viewing microwave radiometer systems. There is a steady growth in active services, and tougher requirements to sensitivity and fidelity of future radiometer systems. Thus it has been decided that the next generation MetOp satellites must include some kind of RFI detection and mitigation system at Ku band. This paper describes a breadboard processor that detects and mitigates RFI on-board the satellite. Thus cleaned data can be generated in real time, and following suitable integration, downloaded to ground at the modest data rate usually associated with radiometer systems.

The increasing problem with Radio Frequency Interference (RFI) in protected radiometer frequency bands has inspired the development and implementation of methods for detecting RFI. With increasing demands for next generation spaceborne radiometers, it becomes necessary to include RFI detection in such systems. Since input to these methods require much more data than traditional radiometer data, and since the downlink capacity for spaceborne systems are limited, RFI detection and mitigation must be implemented on-board thereby maintaining the low downlink data rate. The development of such a system is described in this paper.

A 350 × 350 km area near the Concordia station on the high plateau of Dome C in Antarctica has been mapped by an airborne L-band radiometer system. The area was expected to display a rather uniform brightness temperature close to the yearly mean temperature — well suited for calibration checks for spaceborne instruments like SMOS, Aquarius, and SMAP. The measured brightness temperatures shows unexpected variations like 8 K variation on an East-West profile through Concordia, and in certain cases a slope of almost 1 K per km. Comparing the measured brightness temperature map with bottom topography reveals a convincing correlation. Simulations show that variations in bedrock topography can indeed modulate the brightness temperature appropriately to explain the observed variations.

Design considerations concerning a scanning as well as a push-broom microwave radiometer system are presented. Strict requirements to spatial and radiometric resolution leads to a multiple-beam scanner achieving good sensitivity through integration over many beams, or to a push-broom system where sensitivity is not a problem. Strict requirements to land contamination leads to a dense feed array system. Resource demands, especially power, are important issues, and first estimates are presented.

This paper describes the EMIRAD L-band radiometer, developed in support of the ESA/SMOS mission. The instrument is a fully polarimetric, dual antenna system, built with special focus on antenna accuracy, receiver stability, and detection and mitigation of radio frequency interference (RFI). The EMIRAD system has been installed on three different airborne platforms for measurements of sea surface signatures and salinity, soil moisture, and the homogeneity of the Antarctic SMOS calibration site. The installations are shown in the paper, and some major results for ocean and ice observations are given.

In February 2011, the Polarimetric Airborne Radar Ice Sounder (POLARIS) was flown in Antarctica in order to assess the feasibility of a potential space-based radar ice sounding mission. The campaign has demonstrated that the basal return is detectable in areas with up to 3 km thick cold ice, in areas with up to several hundred meters thick warm shelf ice, and in areas with up to 700 m thick crevassed glacier ice. However, major gaps in the basal return are observed, presumably due to excessive absorption, scattering from ice inclusions in the firn, low basal reflectivity, and the masking effect of the surface clutter. Internal layers are observed down to depths exceeding 2 km. The polarimetric data show that the internal layers are strongly anisotropic at a ridge, where the ice flow is supposed to be highly unidirectional. In case of space-based ice sounding, the antenna pattern cannot offer sufficient surface clutter suppression, but improved clutter suppression has been demonstrated with novel multi-phase-center techniques.

ESA's soil moisture and ocean salinity mission, SMOS, has been found to suffer much more from radio frequency interference (RFI) than expected, and methods for detecting RFI in SMOS data are of vital importance. This paper describes a method using the 3rdand 4thStokes parameters for the purpose. Obvious hot-spots are detected, but also smaller, yet still detrimental RFI, spreading out over for example the ocean, is detected. It is also discussed how detected and flagged samples statistically deviate from their surroundings.

Man-made Radio Frequency Interference (RFI) is an increasingly threatening problem for passive microwave radiometry from space. The problem is presently very evident in L-band data from SMOS, but it is realized that it is already now a problem at other traditional radiometer bands at C, X, and Ku bands. Studies of data from existing radiometer systems have revealed this, and clearly indicates increasing RFI intensity over time. Thus, future missions have to take this into consideration, and dedicated hardware and algorithms to safely detect and mitigate RFI must be included. The design of such an RFI processor is discussed, and resource demands on the spacecraft are indicated.

Several soil moisture and sea salinity campaigns, including airborne L-band radiometer measurements, have been carried out in preparation for the European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission. The radiometer used in this context is fully polarimetric and is capable of detecting radio frequency interference (RFI) using the kurtosis method. Analyses have shown that the kurtosis method generally detects RFI in an efficient manner, particularly concerning pulsed, low duty cycle signals, but it has some shortcomings when it comes to more continuous wave signal types. Hence, other detection methods have been investigated as well. In particular, inspection of the third and fourth Stokes parameters shows promising results—possibly as a complement to the kurtosis method. The kurtosis method, however, cannot be used with SMOS data. Since SMOS is fully polarimetric, the third and fourth Stokes parameter method is an option, and a first assessment using a fully polarimetric SMOS data set looks promising. Finally, a variable incidence angle signature algorithm is introduced, and the possibility of using this as an RFI indicator is discussed.

Several soil moisture and sea salinity campaigns, including airborne L-band radiometer measurements, have been carried out in preparation for the ESA Soil Moisture and Ocean Salinity (SMOS) mission. The radiometer used in this context is fully polarimetric and is capable of detecting Radio Frequency Interference (RFI) using the kurtosis method. Analyses have shown that the kurtosis method generally detects RFI in an efficient manner, even though it has its shortcomings. Hence, other detection methods have been investigated as well. In particular, inspection of the 3rdand 4thStokes parameters shows promising results possibly as a complement to the kurtosis method. The kurtosis method, however, cannot be used with SMOS data. Since SMOS is fully polarimetric, the 3rd and 4th Stokes parameter method is an option, and this has been used on a recent, fully polarimetric SMOS data set. Finally, a discussion of the variable incidence angle signature algorithm, and the possibility of using this as RFI indicator, is carried out.

In support of the European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission, a number of soil moisture and sea salinity campaigns, including airborne L-band radiometer measurements, have been carried out. The radiometer used in this context is fully polarimetric and has built-in radio-frequency-interference (RFI)-detection capabilities. Thus, the instrument, in addition to supplying L-band data to the geophysicists, also gave valuable information about the RFI environment. Campaigns were carried out in Australia and in a variety of European locations, resulting in the largest and most comprehensive data set available for assessing RFI at L-band. This paper introduces the radiometer system and how it detects RFI using the kurtosis method, reports on the percentage of data that are typically flagged as being corrupted by RFI, and gives a hint about geographical distribution. Also, examples of polarimetric signatures are given, and the possibility of detecting RFI using such data is discussed.

ESA has assigned the Technical University of Denmark to develop an airborne P-band ice sounding radar demonstrator. The intention is to obtain a better understanding of the electromagnetic properties of the Antarctic ice sheet at P-band and to test novel ice sounding techniques in preparation for a potential spaceborne ice sounding radar. The airborne system is a coherent, high-resolution and fully polarimetric radar. Aperture synthesis is applied in the along track direction and an experimental surface clutter suppression technique based on a multi-aperture antenna can be applied in the across track direction. In May 2008, a proof-of-concept campaign was organized in Greenland, where data were acquired over the ice sheet. The system proved capable of detecting the bedrock under 3 km thick ice and of mapping the internal ice layers down to a depth of at least 1.3 km. In this paper, the system concept is outlined and first results are presented.

This paper presents the top-level design of an airborne, P-band ice sounding radar under development at the Technical University of Denmark. The ice sounder is intended to provide more information on the electromagnetic properties of the Antarctic ice sheet at P-band. A secondary objective is to test new ice sounding techniques, e.g. polarimetry, synthetic aperture processing, and coherent clutter suppression. A system analysis involving ice scattering models confirms that it is feasible to detect the bedrock through 4 km of ice and to detect deep ice layers. The ice sounder design features a digital signal generator, a microstrip antenna array, a conventional RF-architecture with a central transmitter, four receivers, and internal calibration loops. In 2008 the first data acquisition campaign will take place in Greenland.

The performance of a previously developed algorithm for radio frequency interference (RFI) detection and mitigation is experimentally evaluated. Results obtained from CoSMOS, an airborne campaign using a fully polarimetric L-band radiometer are analyzed for this purpose. Data is collected using two separate integration times, as a result of which sensitivity of the detection algorithm is measured. The impact of RFI on remotely sensed data over land and sea is also presented.

Mapping of sea surface salinity, based on L-band radiometric measurements, is presently investigated as a preparation for space missions. Special concern is on correction for effects caused by the sea surface roughness, and this paper will address two campaigns, LOSAC and CoSMOS, with the aim of investigating these effects. Conclusions from LOSAC are presented, and open issues to be investigated during the presently ongoing CoSMOS campaign are outlined. Finally, the installation and campaign plan for CoSMOS are presented.