HydroGNSS is a European Space Agency (ESA) 2-satellite mission scheduled for launch in the second half of 2025, equipped to continuously operate dual-frequency, dual-polarization GNSS reflectometry (GNSS-R) receivers. It will also utilize a high-rate complex signal mode, called “coherent channel,” to capture both the in-phase and quadrature components of signals reflected at the specular point during most of the duty cycle. This operation will result in a substantial volume of high-resolution GNSS-R data being available for analysis and applications. The three variables to be provided by the HydroGNSS coherent channel are described here and validated with CYGNSS raw intermediate frequency (IF) signals. The coherence coefficient (CC) and the normalized amplitude (NA), developed from the peak phasors using 4-ms coherent integration time, were compared to the “full entropy” available in the CYGNSS calibrated raw IF product. NA has a similar sensitivity to water surfaces as the full entropy and is not significantly affected by the coherent integration time. CC exhibits a higher sensitivity to small water bodies, yet it strongly depends on the coherent integration time. We also present a new product, the high sampling rate reflectivity (HSRR). It is here defined and compared to CYGNSS${L}1$low rate reflectivity as well as to the high sampling rate (hsr) CYGNSS calibrated raw IF reflectivity, showing a correlation above 0.92. Its effectiveness has been further validated by a physical model, and its uncertainty was preliminarily assessed using data from two nearby tracks. The results demonstrate that HSRR can be a valuable tool for retrieving geophysical parameters, offering a much finer resolution than the 1–2-Hz product.

With the evolution of Global Navigation Satellite System (GNSS), more GNSS satellites and civilian signals are available for GNSS Reflectometry (GNSS-R). Developments of new onboard processing strategies can improve the observation performance of spaceborne GNSS-R. To this end, this article proposes a new processing method by coherently combining reflected Global Positioning System (GPS) III L1 C/A and L1C signals. By exploiting the additional signal component, the signal-to-noise ratio of the reflected signal can be significantly improved. Moreover, taking advantage of the narrower auto-correlation function of the combined signal, the spatial resolution and the performance on geophysical applications can be significantly improved. The proposed method has been validated by processing cyclone GNSS (CYGNSS) raw intermediate frequency data including the direct and reflected signals from GPS III satellites. The results indicate that the signal-to-noise ratio (SNR) of the combined reflected waveform can be improved by ~2 dB compared to the L1 C/A waveform. Moreover, the SNR of the combined signal can be improved more efficiently using a longer coherent integration interval compared to the L1 C/A signal. Preliminary altimetric results demonstrate a 35.3%-61.6% improvement in the ranging standard deviation, and a 22.4%-64.4% improvement in the median absolute deviation, compared to L1 C/A measurements. Additionally, the correlation coefficient between combined measurements and wind speed improves by 26.3% on average compared to L1 C/A measurements, and 45.7% for high winds. This article presents a novel GNSS-R onboard signal processing method with improved performance, which can provide a reference for the design of future GNSS-R instruments.

This paper presents de development plans of a combined P&L-band reflectometry sensor using signals of opportunity.

The use of Signals of Opportunity (SoOp) is an advantageous way to sense the Earth and ocean surface in a passive bi-static radar configuration, as it allows for smaller sensors compared to active radars. The signals transmitted by the navigation satellites (GNSS) are a good example of SoOP. Several missions using GNSS signals have been launched, e.g. . Using GNSS reflectometry it is possible to obtain estimates of ocean roughness, cryosphere, inland waters or soil moisture, e.g. Other missions using GNSS signals are also being prepared, as for instance, ESA’s second Scout Mission, HydroGNSS [9], which is targeting soil moisture, or ESA’s Pretty mission devoted to altimetry.

FSSCAT mission was the 2017 ESA Sentinel Small Satellite (S^3) Challenge winner, and the Copernicus masters competition overall winner, and it will be launched in late March 2020. FSSCAT data will provide soil moisture data, sea ice cover and coarse resolution sea ice thickness. FSSCat will be launched for Kourou Space port on June 18th, 2020, 10:51 PM local time. MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) campaign is a one-year long field experiment to study the climate system and the impact of the climate change in the Arctic sea. GNSS-R data from the second leg has been received recently. At the conference the first results of the FMPL-2 payload (combined GNSS-R and microwave radiometer instrument) on board FSSCat will be presented. Preliminary results on the PYCARO-2 GNSS-R instrument in MOSAIC, and model results fed with in-situ auxiliary data are presented in this paper.

In February 2019 a Project Authorization Request was approved by the Institute of Electrical and Electronics Engineers (IEEE) Standards Association with the title “Standard for Global Navigation Satellite System Reflectometry (GNSS-R) Data and Metadata Content”. A Working Group has been assembled to draft this standard with the purpose of unifying and documenting GNSS-R measurements, calibration procedures, and product level definitions. The Working Group (http://www.grss-ieee.org/community/technical-committees/standards-or-earth-observations/) includes members, collaborators, and contributors from academia, international space agencies, and private industry. In a recent face-to-face meeting held during the ARSI+KEO 2019 Conference, the need was recognized to develop a standard with a wide range of operations, providing procedure guidelines independently of constraints imposed by current limitations on geophysical parameters retrieval algorithms. As such, this effort aims to establish the fundamentals of a potential virtual network of satellites providing inter-comparable data to the scientific community.

This article assesses the ocean altimetry performance of spaceborne Global Navigation Satellite Systems reflectometry (GNSS-R) by processing the raw data sets collected by the Cyclone GNSS (CYGNSS) constellation. These raw data sets, i.e., the intermediate frequency signal streams before any receiver processing, are processed on the ground with a software receiver, from which the reflected waveforms of GPS L1, Galileo E1, and BeiDou-3 B1 band open service (OS) signals are generated following the conventional GNSS-R approach. By using different retracking algorithms, the bistatic delays of the reflected signals are derived from these waveforms, in which the retracking biases are removed with the specular point (SP) delay and power information computed from the corresponding waveform model. After applying a set of standard delay corrections, the bistatic delay observations are converted into sea surface height (SSH) measurements and compared with the mean SSH model. Both the random error (precision) and systematic effects (accuracy) are characterized with intratrack and intertrack analyses of the bistatic delay measurements. The two-way ranging precision can reach up to 3.9 and 2.5 m with 1-s GPS and Galileo group delay measurement (a factor of ~2 better for altimetry solution), and its evolution with the signal-to-noise ratio shows good consistency with the theoretical model. A significant delay dispersion of 3.0 m between different tracks is found, which is mainly attributed to the receiver orbit error and ionospheric correction residuals. These results can provide useful inputs for the development of future GNSS-R missions dedicated to ocean altimetry applications.

This work aims to demonstrate the applications of spaceborne Global Navigation Satellite System reflectometry (GNSS-R) over inland waters and wetlands. Raw samples of the GNSS signals reflected from lakes, rivers and wetlands have been recorded occasionally by the TechDemoSat-1 (TDS-1) and Cyclone GNSS (CYGNSS) missions. Strong coherent reflections have been found in the GNSS-R signals from open inland water bodies (lakes and rivers), which would make possible to perform precise surface altimetry measurements using both group delay and carrier phase from reflected signals. In addition, it is also found that GNSS signals reflected off densely vegetated wetlands also present some coherent features from the evolution of their carrier phase, showing the potential of the GNSS-R technique to monitor extremely dense wetlands from spaceborne platforms.

In global navigation satellite systems reflectometry (GNSS-R), the autocorrelation property of the transmitted GNSS signal is an important factor in the delay-Doppler map of the scattered power. The autocorrelation functions (ACFs) of the GPS Level 1 (L1) coarse/acquisition signals exhibit sidelobes. For some of the pseudorandom noise (PRN) codes, the high-amplitude sidelobes are located within one chip from the main lobe and, thus, broaden or narrow its width. These PRN-dependent ACF deviations can introduce significant biases into the GNSS-R scatterometric observables and the wind speed measurements. Simulation results for Cyclone GNSS (CYGNSS) mission show that the ACF deviation induced wind speed error can be larger than 10% (e.g., 2-3 m/s for 20 m/s and 7-8 m/s for 40 m/s wind speeds). These effects can be corrected efficiently by applying empirical factors on the CYGNSS L1 observables.

This work is to demonstrate spaceborne altimetry over sea ice using coherent component of reflected Global Navigation Satellite System (GNSS) signal. The raw samples of sea ice reflected GNSS signal collected by the UK TechDemoSat-l (TDS-l) mission are processed. Strong coherent components are found in sea ice reflected GNSS signal received in space at different elevation angles, which would make it possible to perform precise surface altimetry measurements using the carrier phase information of the reflected signals. In addition, the coherent reflected signals can be integrated coherently for a longer period to increase the signal to noise ratio, which would make it possible to demonstrate the interferometric GNSS-R (iGNSS-R) altimetry technique in space without very high gain antenna. In this presentation, the altimetric results of coherent GNSS reflections with both carrier phase and code phase will be discussed.

We present a new passive bi-static radar measurement concept that employs digital satellite TV signals transmitted from geostationary orbit as signals of opportunity to measure precipitation. We also present experimental results using artificial targets, and provide results on measured Doppler frequencies as well.

This paper analyzes the ocean altimetry precision of global navigation satellite systems' reflectometry (GNSS-R) by characterizing the noise statistics of the measured waveform. For this purpose, we first investigate the dependence of the altimetry precision on the statistics of the observed waveform and then derive an analytical model of the waveform statistics after incoherent averaging. The main data set used for altimetry analysis and model validation is the GPS L5 signals obtained from an airborne experiment. Two different delay estimators, based on the leading-edge derivative (DER) and the waveform fitting (FIT) over the leading edge, have been implemented. Later, the relationship between the statistics of the observed waveform and the altimetry precision is derived and validated for both the estimators with the airborne data. Then, the analytical model of the statistics of the incoherently averaged waveform is built from the correlation properties of the complex waveform, and also validated with both airborne and the TechDemoSat-1 spaceborne data. After that, the proposed waveform statistics and altimetry precision models are applied to spaceborne cases with different orbit altitudes. The altimetry performance of different onboard processing methods, i.e., conventional GNSS-R and interferometric GNSS-R, and delay estimators, i.e., DER and FIT, are preliminarily assessed. Finally, the dependence of altimetry precision on different parameters is analyzed and a simplified model of altimetry precision is proposed for the spaceborne case.

Characterizing, understanding, and projecting changes in atmospheric methane and terrestrial water storage require information about wetland dynamics, which remains a major gap in existing knowledge. Despite recent advances in satellite monitoring techniques, dynamic wetland mapping needs to be improved for more accurate global inventories and also to monitor variabilities at sub-km scale over multiple decades. It has been shown that Global Navigation Satellite Systems (GNSS) Reflectometry (GNSS-R) signatures off inundated wetlands can be identified under different vegetation conditions including a dense rice canopy and a thick forest with tall trees, where optical sensors and monostatic radars provide limited capabilities. In this study, we will further investigate the capabilities of the GNSS-R technique for wetland monitoring from aircraft platforms.

This work is to analyse the ocean altimetry precision of Global Navigation Satellite Systems Reflectometry (GNSS-R) based on the statistics of observed waveform. The GPS L5 signals obtained from an airborne experiment are used for this study. The altimetry precision is analysed for two specific algorithms, based on the leading edge derivative (DER) and the leading edge fitting (FIT), in which the relationship between the altimetry precision and the waveform statistics is established and validated. Then, we introduce an analytical model of the statistics of the incoherently averaged waveform, which has been validated with both airborne and spaceborne data. Finally, as an example, the altimetry precision is predicted for the GEROS-ISS mission, and preliminary results are presented.

Since the nadir 1-second altimetry precision was first estimated to be of 56 cm when the PARIS concept was developed back in 1993 (it was assumed the interferometric processing of GPS P-code signals and a 4×4 m×m receiving antenna at 700 km orbital altitude) [1], many detailed analyses and experiments have been conducted leading to far more optimistic values, as low as some 15 cm (using the interferometric processing and a 1 m2antenna from 400 km altitude). This paper presents the instrument and concept advances that have allowed such improved expectations.

The Software PARIS Interferometric Receiver (SPIR) was conceived as a multiple beam-forming GNSS-Reflectometry receiver capable of implementing different signal processing strategies (clean-replica, interferometric, etc.) in order to demonstrate the synoptic capabilities for sea-surface altimetry using the interferometric GNSS-R technique. The instrument has been designed as a 16-channel very-high speed (320 MB/s) hardware recording receiver followed by a software post-processor, implementing the beam-forming and signal processing. The presence of 16 channels together with the beam-forming capabilities requires to characterize the quantization offsets, instrument time-keeping and relative instrumental delays between the different channels in order to have a well-functioning instrument. In this paper we present several calibration aspects of SPIR.

We present in this paper the work done to test the synoptic capabilities of the GNSS-R interferometric technique as a means towards sea surface altimetry estimation, which is an integrated part of the assessment of the GEROS-ISS mission. For this purpose, a new software receiver has been developed and tested: SPIR. With the lessons learned after a first flight campaign, some system modifications were performed and a second experimental campaign has been recently carried on. Initial results show interferometric waveforms that present the quality required for altimetric analysis.

The Software PARIS Interferometric Receiver (SPIR) is a multichannel GNSS-R recording receiver. It is capable to record the GNSS signals at L1, L2 or L5 bands from eight up-looking and eight down-looking antenna elements simultaneously at a rate of 80 MHz. A software post-processor processes the recorded data off-line to obtain altimetric estimates. Its development has been carried out in order to validate experimentally the synoptic capabilities of GNSS-R using the PARIS Interferometric Technique and to allow the comparison of different GNSS-R processing techniques on exactly the same set of recorded data. The paper presents the instrument's main characteristics and preliminary results.

This paper revises the precision of altimetric measurements made with signals of the Global Navigation Satellite Systems (GNSS) reflected (GNSS-R) off the sea surface. In particular, we investigate the performance of two different GNSS-R techniques, referred to here as the clean-replica and interferometric approaches. The former has been used in GNSS-R campaigns since the late 1990s, while the latter has only been tested once, in 2010, from an 18-m-high bridge in static conditions and estuary waters. In 2011, we conducted an airborne experiment over the Baltic Sea at 3-km altitude to test the interferometric concept in dynamic and rougher conditions. The campaign also flew a clean-replica GNSS-R instrument with the purpose of comparing both approaches. We have analyzed with detail the data sets to extract and validate models of the noise present in both techniques. After predicting the noise models and verifying these with aircraft data, we used them to obtain the precision of altimetric measurements and to extrapolate the performance analysis to spaceborne scenarios. The main conclusions are that the suggested noise model agrees with measured data and that the GNSS-R interferometric technique is at least two times better in precision than a technique based on using a clean replica of the publicly available GPS code. This represents a factor of at least four times finer along-track resolution. A precision of 22 cm in 65-km along-track averaging should be achievable using near-nadir interferometric GNSS-R observations from a low earth orbiter.

A bistatic radar at X-band (11 GHz) using opportunity signals (Passive Reflectometry and Interferometry System (PARIS) concept implementing the interferometric technique) has been developed and tested in a coastal-based experimental setup. Digital satellite TV signals broadcast from geostationary orbit have been used as sources of opportunity, and correlation waveforms have been collected at different receiver bandwidths. Calibration algorithms to compensate instrumental errors have improved our observables and allowed us to obtain delay measurements with a precision of about 10 cm for wind speeds in the range of 3 m/s. A statistical analysis of the measurement noise is used to determine the quality of the obtained observables. This paper also discusses the opportunities of the PARIS concept applied at higher frequency band and with stronger signals.

Reflectometry using Global Navigation Satellite System's signals of opportunity (GNSS-R) was originally conceived for mesoscale altimetry [1], although its applicability to sea state determination, soil moisture, vegetation, snow monitoring... has already been demonstrated. In December 2012 the Phase A studies of ESA's PAssive Reflectometry and Interferometry System In-orbit Demonstration (PARIS IoD) mission ended. In conventional GNSS-R the GNSS signals scattered over the Earth's surface are cross-correlated with a locally generated replica of the transmitted signal shifted in frequency (Δfd) and in delay (Δτ). PARIS is called an interferometric GNSS-R (iGNSS-R) system because the direct and the scattered signals are cross-correlated in order to use the whole signal's bandwidth, and improve the altimetric precision, despite the large bandwidth signals are not publicly available. This work presents a methodology to evaluate the performance of iGNSS-R altimeters. It is then applied to a PARIS IoD-like case, in which the receivers' bandwidths have been optimized in terms of altimetric resolution.

Tracking, in radar altimetry, is the positioning of the waveforms in the correlation window. This letter presents a tracking strategy in spaceborne altimetry using global navigation satellite system reflectometry. First, the tracking procedure is illustrated, and the tracking parameters are discussed one by one: the determination of the correlation window, the accuracy of specular delay guess, and the tracking-refresh period. Based on the results, the proposed European Space Agency Passive Reflectometry and Interferometry System In-Orbit Demonstrator tracking case study is examined.

We report preliminary results of an aircraft experiment aimed to proof the PARIS Interferometric Technique. The experiment was performed in the Gulf of Finland during a two hours flight. We installed a PARIS Interferometric Receiver together with a GOLD-RTR instrument to collect reflected C/A, P(Y) and M-code GPS signals. The collected data has been analyzed to produce altimetric observables with both techniques.

This paper evaluates the potential use of reflected signals from Global Navigation Satellite Systems as a source of opportunity for the retrieval of absolute ellipsoidal heights over sea ice. Accurate estimation of the surface level would be helpful for the determination of the ice thickness, a key parameter for classification and characterization of sea ice masses. Our analysis is based on altimetric estimations from the coherent differential phase between direct and both cross- and co-polar reflected signals. For this purpose, GPS waveforms have been collected from a fixed platform in Greenland, monitoring the complete process of sea ice formation and melting during a 7-month period. The variability of coherent phase samples and polarimetric measurements are compared with in situ observations to make a realistic rough characterization of the ice cover. The retrieved sea ice surface height estimates are then evaluated against an Arctic tide model, ice surface temperature from moderate-resolution imaging spectroradiometer, and the laser altimetry product from ICESat.

We present in this paper an empirical approach for the characterization of the internal layering of dry snow masses by means of GNSS-R. A forward model has been designed for reconstructing reflected waveforms given a dry snow profile and geometry (elevation and elevation-rate), as a sum of multiple responses from different layers. To extract the internal information, Fourier transforms of time series of waveforms are computed to generate lag-holograms. The frequency stripes that appear are related to the depths of the contributing snow layers. The same analysis has been done with real data, showing with agreement with the models.

The use of opportunity signals to make altimetric measurements is known as the PARIS (PAssive Reflectometry and Interferometry System) concept. Signals transmitted by the GPS satellite constellation reach the PARIS receiver by the direct path and are collected by a zenith looking antenna. Signals reflected on the Earth's surface reach the PARIS receiver as well and are collected by a nadir looking antenna. The instrument measures the relative delay between the instants of arrival of the direct and reflected signals. By knowing the positions of transmitters and receivers the distance to the scattering surface can be retrieved. The presented work aims to clarify if one-bit correlation can be successfully used in the PARIS-IOD, and under what limitations. It can be concluded that an upper bound has been found for the SNR of the signals at the PARIS-IOD if one-bit quantization is used and a linear cross-correlation with the same shape as the analog correlation is desired. That is, it is not possible to increase the signal SNR at any desired level without distorting the cross-correlation waveform if one-bit digitalization is used. Simulation results have been presented confirming the upper bound for the SNR of the signals.

GPS reflected signals have become a source of opportunity for remote sensing of the Earth's suface. In this work, we present several capabilities of this technique in two different polar environments: Greenland and Antarctica. The first part is dedicated to the retrieval of sea-ice properties, giving emphasis to the study of the coherent phase for altimetric and roughness estimations, and polarimetric measurements for the determination of the ice salinity variation. The results show good agreement with a tide model and daily ice charts. On the second part, some preliminary results and analysis strategies to retrieve dry snow signatures are presented.

A proof-of-concept instrument for PARIS-IOD, based on a full-custom dedicated GNSS-Reflections receiver has been developed, and the novel interferometric concept tested in several experiments using signals generated by a SPIRENT equipment. The preliminary analysis has resulted in the detection of 1-cm delay-jumps, using 33 group-delay observables of 1 second, with an associated dispersion of the order of 2-cm. A signal-to-noise degradation of the order of ~3 dB with respect to the one expected for the Bridge Experiment would keep the 1-second sigma error below 3-cm.

This paper describes AMIRAS, an airborne demonstrator of the Microwave Imaging Radiometer with Aperture Synthesis, which is the instrument onboard ESA's Soil Moisture and Ocean Salinity (SMOS) mission. The main electrical, mechanical, thermal, and control elements of the demonstrator are shown, together with its capabilities and performances as demonstrator of the spaceborne instrument. AMIRAS main tests inside an anechoic chamber, field ground experiments, and its first two maiden flights are reported, and some results of these tests are highlighted. AMIRAS will further be used in some calibration and validation campaigns of the SMOS mission.

In this paper, some results of the MIRAS-SMOS demonstrator campaigns are presented. The follow two campaigns were held: an image validation campaign at IRTA side and a flight demonstrator campaign at Finland. The ultimate objective of the airborne demonstrator is to demonstrate its imaging capabilities by applying improved calibration and inversion algorithms to natural low-contrast targets.

The technological aspects of the Altimetric and Scatterometric Applications of PARIS (ASAP) sensor are presented in this paper. This sensor is based on the PARIS concept, which makes use of GPS signals reflected on the ocean's surface in order to measure the surface's properties (altitude and roughness). The ASAP instrument is a hardware real-time PARIS receiver with the aim of being an intermediate step between the airborne GOLD-RTR receiver developed at our institute and a future spaceborne PARIS instrument.

SMOS, acronym for Soil Moisture and Ocean Salinity, is the second selected opportunity mission on "The Living Planet Program: Earth Explorer Opportunity Missions" of the European Space Agency (ESA) [1]. The MIRAS (Microwave Imaging Radiometer with Aperture Synthesis) is the single SMOS pay- load, which is compounded of 69 L-band receivers to form a Y shape interferometer with full on-board calibration capability. The Spanish company EADS-CASA is currently leading the development of a Small scale Airborne prototype of the MIRAS (SAM), in the frame of the MDPP-3 project (MIRAS Demonstrator Pilot Project, stage 3) sponsored by the ESA. Several European institutions, including the Polytechnic University of Catalonia, are participating in the development of the MDPP-3 instrument and test campaigns. The demonstrator consists of 12 receivers called LICEF (4 per arm), 1 reference radiometer (NIR) and includes the same internal calibration system scheme foreseen for MIRAS. The instrument has been designed to be flown in the Skyvan of the LST/HUT (Laboratory of Space Technology, Helsinki University of Technology), where several airborne campaigns over land and sea will be undertaken in order to asses the capability of SMOS calibration and retrieval algorithms to provide soil moisture and ocean salinity.

End-to-end calibration of the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) radiometer refers to processing the measured raw data up to dual-polarization brightness temperature maps over the earth's surface, which is the level 1 product of the Soil Moisture and Ocean Salinity (SMOS) mission. The process starts with a self-correction of comparators offset and quadrature error and is followed by the calibration procedure itself. This one is based on periodically injecting correlated and uncorrelated noise to all receivers in order to measure their relevant parameters, which are then used to correct the raw data. This can deal with most of the errors associated with the receivers but does not correct for antenna errors, which must be included in the image reconstruction algorithm. Relative S-parameters of the noise injection network and of the input switch are needed as additional data, whereas the whole process is independent of the exact value of the noise source power and of the distribution network physical temperature. On the other hand, the approach relies on having at least one very well-calibrated reference receiver, which is implemented as a noise injection radiometer. The result is the calibrated visibility function, which is inverted by the image reconstruction algorithm to get the brightness temperature as a function of the director cosines at the antenna reference plane. The final step is a coordinate rotation to obtain the horizontal and vertical brightness temperature maps over the earth. The procedures presented are validated using a complete SMOS simulator previously developed by the authors.

This paper describes a new method to compensate the Faraday rotation in polarimetric radiometric measurements under the assumption that the polarimetric brightness temperature matrix of the target is diagonal. Simulations results of how this method can be used within the Soil Moisture and Ocean Salinity mission and the Microwave Imaging Radiometer with Aperture Synthesis imaging radiometer are presented.

An interferometric radiometer prototype at 1.4 GHz was successfully demonstrated. The system was developed for the image validation of MIRAS (Microwave Imaging Radiometer with Aperture Synthesis). The instrument, image processing procedure, and measurement results are presented. The future development of the system is discussed.

The L-band Microwave Imaging Radiometer with Aperture Synthesis (MIRAS), scheduled to be flown as single payload on board the European Soil Moisture and Ocean Salinity (SMOS) mission, has a very wide field of view and synthesizes narrow beams by means of two-dimensional (2-D) interferometry, the same concept used in radio astronomy. Wide field of view is indeed a key feature of this radiometer, which leads naturally to the measurement of the full vector of brightness temperatures of the image. This paper analyzes the theory of polarimetry in the 2-D wide-field-of-view microwave interferometry and describes the way MIRAS will measure the polarimetric brightness temperatures.