Josep Closa

Generation of Advanced ERS and Envisat Interferometric SAR Products Using the Stable Point Network Technique

The advanced differential interferometric SAR techniques (A-DINSAR), based on time series of SAR images, are powerful geodetic tools for land deformation monitoring. This paper, which is focused on a particular A-DINSAR technique, named Stable Point Network, concisely outlines its characteristics and describes its products: average deformation maps, deformation time series, and the maps of the residual topographic error used to precisely geocode the A-DINSAR products. Furthermore, it illustrates the performance of the technique on a test area located in Barcelona, Spain. From this experiment, interesting features are highlighted: the capability to cover wide areas and at the same time measuring thin infrastructures, such as the main dike of the port; the good agreement between the deformation velocities and the reference values coming from leveling campaigns; the high sensitivity of the A-DINSAR estimations, which can measure millimeter-level periodical deformations due to thermal dilation, and the precise geocoding of the A-DINSAR products.

ASAR ERS interferometric phase continuity

For ten years, a long history of data was acquired by the SAR sensors on the satellite ERS-1 and ERS-2 offering a wide range of interferometric applications. In 2002, the more advanced satellite ENVISAT was launched. The SAR on board on ENVISAT (ASAR) can continue the success of the remote sensing mission of the ERS satellites and preserve or even increase the value of the archived ERS data. The subject of this study is to demonstrate the continuity of the interferometric measurements by the combination of the SAR scene of the different sensors to interferograms (cross interferometry).

Radiometric Performance of the SMOS Reference Radiometers—Assessment After One Year of Operation

In this paper, we present an analysis of the radiometric performance of the three 1.4-GHz noise injection radiometers of the European Space Agencys Soil Moisture and Ocean Salinity (SMOS) satellite. The units measure the antenna temperature, which contributes to the average brightness temperature level of SMOS retrievals. We assess the radiometric resolution of the receivers, the similarity between their measurements, and their thermal stability. For these purposes, we use SMOS measurement data gathered during the first year of the orbital operations of the satellite, which was launched in November 2009. The main results from the analysis are that the units meet the design requirements with a margin. Also, we present a new thermal model for the radiometers to further enhance their stability.

ASAR instrument performance and product quality status

This paper presents the main characteristics of the advanced synthetic aperture radar (ASAR) instrument on board ENVISAT, ASAR products, the challenges in the ASAR calibration and product validation, the methodology used to perform the sensor performance monitoring and product calibration based on the special ASAR features and dedicated calibration sites and finally a summary on the product quality status will also be provided.

Calibration and early results of the ASAR on ENVISAT

This paper presents the approach for the in-flight calibration of the ENVISAT-1 ASAR and the verification of the ground processing facility PF-ASAR during the commissioning phase. The philosophy presented is a logical progression from the experience gained during calibration of the ERS SARs. The ASAR has a comprehensive internal calibration loop, which is described distinctly from the external calibration and characterisation. The antenna patterns of the various beams have been fully measured during on-ground flight-model testing and have been used for initial performance predictions. In-flight characterisation of the main beams is performed over the South American rainforest. As for ERS, absolute gain calibration is achieved using three fixed and one transportable precision calibration transponders situated in the Netherlands. These transponders are also capable of recording the azimuth beam patterns and supporting the external characterisation mode of ASAR.

Smos payload performance assessment

The performance requirements of the SMOS payload are demanding in terms of spatial resolution, accuracy, stability and precision, all critical to fulfill its scientific objectives. For this reason a commissioning plan for MIRAS was carefully devised to verify, calibrate and characterize all instrument parameters which could have an impact on its performance. This presentation describes the most important results from the instrument commissioning phase.

Prelaunch Estimation of Radiometric Resolution and Stability of SMOS Zero-Baseline Radiometer in Anechoic Chamber

The purpose of the Soil Moisture and Ocean Salinity (SMOS) mission is to measure soil moisture and sea surface salinity (SSS). The measurement of SSS using microwave radiometry requires a very sensitive instrument. In SMOS, the image is formed using the interferometric technique complemented by the average brightness temperature, or zero baseline, to set the absolute level of the image. Therefore, the measurement of the zero baseline is very critical for the success of the mission. In this paper, the radiometric resolution and stability of the radiometers dedicated to the measurement of zero baseline on SMOS are estimated. The results of a measurement campaign carried out in an anechoic electromagnetic compatibility chamber are used. The results show that the zero-baseline radiometers have the potential for relative accuracy better than 20 mK, depending on the integration scenario, satisfying the mission requirement for SSS retrieval.

SMOS instrument performance and calibration

This paper presents the progress made in the calibration and image reconstruction of the brightness temperature data provided by the SMOS mission of the European Space Agency. This progress has been made thanks to the learning through the accumulation of results since the launch of the satellite. Current performance of the payload on-board SMOS, the MIRAS interferometer, our main findings on its behavior and open lines of investigation are included in this contribution.

Evaluation of the Internal Calibration Methodologies for Spaceborne Synthetic Aperture Radars with Active Phased Array Antennas

This paper presents a novel approach in the instrumental error analysis of Synthetic Aperture Radars (SAR) based on active phased array antennas (APAA). A residual post-calibration error exists due to differences between the calibration and operational excitations of the transmit/receive modules (TRMs) for those source errors that are monitored by the internal calibration facility. Analytical expressions are derived for the residual post-calibration errors and validated through intensive simulations of some instrumental errors for a specific sensor architecture. Alternative internal global calibration strategies are proposed to reduce the impact of the post-calibration error. The simulations show that the proposed elevation dependent calibration can provide a substantial reduction of the post-calibration errors even in the case of relaxed tolerance of the TRM weight setting errors.

Internal calibration strategies for space-borne synthetic aperture radars with active phased array antennas

This paper proposes an analytical formulation of the instrumental errors in multilevel hierarchic SAR architecture equipped with active phased array antennas. The basis of the study is the derivation of the so called post-calibration errors, which remain as residual error contributions after the application of a dedicated internal calibration procedure. The limitations of the current internal calibration approaches for the-state-of-the-art space-borne SAR missions are analyzed and alternative internal global calibration strategies are proposed to reduce the impact of the post-calibration error. Numerical simulations of instrumental errors are presented to evaluate the different proposed calibration procedures.