Sentinel-1 (S-1) is the European flagship SAR mission initiated by European Space Agency and the European Commission. It is a constellation of two C-band twins satellite providing backscatter globally. The calibration and overall SAR performance of the mission is continuously assessed by the S-1 Mission Performance Center being a joint venture of European experts in their domain under ESA‘s supervision. This paper addresses the Copernicus Sentinel-1A/B mission’s SAR calibration and overall performance indicators after 8 years cumulated operation having in sight S-1A approaching its expected lifetime of 7 years. Sentinel-1 uses predefined observation scenario to provide a high revisit frequency and systematic global SAR image coverage. This is mainly based upon the operational use of the TOPS (Terrain Observation with Progressive Scans in azimuth) SAR imaging mode allowing to achieve a wide swath with a relatively high resolution. In particular, we present results of the SAR system performance analysis focusing on the instrument stability, the radiometric, geolocation accuracy, the Noise Equivalent Sigma Zero (NESZ) and all interferometric performance indicators. In addition, we discuss the Sentinel-1A/B SAR cross-calibration and the evolution of the system in the near future.

Sentinel-1 (S-1) is a constellation of two C-band SAR satellites [1] whose development is co-funded by the European Space Agency (ESA) and the European Commission (EC) as part of the Copernicus space program. S-1A was launched in May 2014 followed by the S-1B unit two years after. The constellation is operational since September 2016 after the successful commissioning of the second unit. This paper provides an update of the constellation performance and recalls the last result achieved in terms of radiometric and geometric accuracy.

This paper compares the classification capability of data acquired in hybrid and dual linear polarization mode over the Chelmsford area, United Kingdom, from RISAT-1 C-band satellite. Support vector machine based supervised classification is used in the study and accuracy is assessed over the validation pixels. The hybrid-pol RH/RV combination shows better classification accuracy over linear pol HH/HV combination by 2.5 %. Overall classification accuracy is increased to 90% over the given area when Stokes parameter are added to the polarization combination.

This paper addresses the results of the instrument and product performance verification, radiometric and geometric calibration achieved since the end of the respective Sentinel-1 A and B commissioning phases.

Synchronous with RISAT-1 and RADARSAT-2 passes, corner reflectors (CR) were mounted for the evaluation of radiometric calibration of RISAT-1 compact polarimetric SAR data. Based on the CRs response on SLC images, RISAT-1 calibration constant, PSLR/ISLR, resolution, channel imbalance and cross-talk were analyzed and compared with that of product specifications. A difference of 0.5 to 1.5 dB is observed between product and estimated calibration constant K. The resolution and PSLR/ISLR are better than the specification of the product. Backscattering coefficient and compact polarimetric parameters of RISAT-1 were compared with RADARSAT-2 simulated compact polarization. The large difference in sigma-0 is observed for water and sand features due to high value of noise-equivalent-sigma-zero of RISAT-1. Similarly, some differences are observed between RISAT-1 estimated compact polarimetric parameters (m, m c , δ, χ, axial ratio, CPR) and that of RADARSAT-2 simulated compact data.

This paper addresses the results of the instrument and product performance verification, radiometric and geometric calibration achieved during the since commissioning and routine phase.

The long-term external radiometric calibration of spaceborne SAR systems is an important task as this gives information about the instrument in an extended time window, up to the whole mission lifetime, and can reveal slow or small trends that may be hardly noticeable in the short term. Conventional methodologies, such as the ones based on transponders or corner reflectors, provide reliable measures, but may be affected by failures themselves and this may cause difficulties for long-term analyses. Vicarious calibration techniques, that rely directly on SAR data, have proven to have a comparable level of reliability, with cost effectiveness and with no interference to the mission or to the routine operation of the instrument. Such techniques are based on the Persistent Scatterers (PS-CAL) or on the ocean. This paper, first presents a brief overview of the SAR calibration techniques, then reports the outcomes of the PS-CAL on a large number of ERS and ENVISAT ASAR data, covering several years, within the missions lifetime. The analysis is done on the basis of the estimated external calibration time series and includes comparison with transponders, the Amazon rain forest and ocean-based radiometric calibration.

The Advanced Synthetic Aperture Radar (ASAR) on- board Envisat operated successfully for just over 10 years until the failure of Envisat in April 2012. ASAR was ESA's very first deployment of a C-band phased- array antenna, allowing extended imaging capacity in comparison to its ERS SAR predecessors. As such it operated in various acquisition modes - Image (IM), Alternating Polarisation (AP), Wide Swath (WS), Global Monitoring (GM), and Wave (WV). For IM and AP modes there was a selection of 7 swaths with swath width from 100 km to 56 km: IM was single- polarisation, while AP was dual-pol, offering a choice from HH&VV, HH&HV, or VV&VH. WS and GM modes had a total swath width of 405 km based on the combination of 5 sub-swaths. WV acquired imagettes of 10 km by 10 km every 100 km along the satellite track. This paper is a look back to the 10 years of ASAR operations, covering topics such as the ASAR Instrument (characteristics, acquisition modes, product tree and observation scenario), Instrument Calibration and Performance Verification (including instrument stability, internal calibration, external calibration, absolute radiometric calibration, localisation accuracy, absolute geolocation accuracy, performance verification and product calibration), ASAR specific missions (wave and polarimetric), particular ASAR events such as

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The European Space Agency (ESA) ERS-2 Synthetic Aperture Radar (SAR) has successfully operated for more than 13 years (since April 1995). The performance of the ERS-SAR is routinely assessed via a variety of quality assessment and calibration measures. This paper gives the latest ERS-2 SAR quality assessment and calibration results, including elevation antenna pattern estimation and monitoring, updates to ERS-2 SAR internal calibration and stability, noise equivalent radar cross-section measurements, updates to the ERS-2 nominal replica pulse correction table and image localisation results. Equations are given for the calculation of distributed and point target radar cross-sections from the multi- look ground range detected ERS-2.SAR.PRI/IMP and the single-look slant range complex ERS- 2.SAR.SLC/IMS products. Also given are ERS-2 attitude and SAR Doppler variations following the change from three to one gyroscope operations in February 2000 and the change to gyro-less operations in February 2001. A brief description is given of the evolution and harmonisation during 2006 of ERS SAR products from VMP to PGS-ERS processors and to the same specification as Envisat ASAR product. Finally a recent problem with the sampling window start times of some ERS-2 SAR acquisitions is described.

Within the ALOS Data European Node (ADEN) the verification of PALSAR products is an important and continuing activity, to ensure data utility for the users. The paper will give a summary of the verification activities, the status of the ADEN PALSAR processor and the current quality issues that are important for users of ADEN PALSAR data.

Following the commissioning phase of the Advanced Synthetic Aperture Radar (ASAR) instrument on-board EnviSat decision was taken to re-deploy three of the existing four ASAR Transponders, specially procured for this instrument, from locations within The Netherlands to sites all over the world. The Re-Deployment of the ASAR Transponders describes a major activity in order to maintain the high level of ASAR calibration. Furthermore, for the first time, it allows ESA to perform around orbit calibration of the EnviSat ASAR instrument. We present the initial and final Deployment of all four EnviSat ASAR Transponders and explain the objectives and the strategy together with the challenges faced installing the ASAR Transponder instruments at very remote locations including Indonesia and the Arctic. The excellent results of the latest calibration figures show the success of this campaign.

ALOS, an enhanced successor of the Japanese Earth Resources Satellite 1 (JERS-1), was launched from JAXA's Tanegashima Space Center in January 2006. An important contribution to the ALOS mission is the verification of PALSAR products to be distributed by the European ADEN node using the PALSAR processor developed by JAXA. A total of 28 ALOS PALSAR products have been analysed with respect to radiometric, geometric and polarimetric quality (including effects of Faraday rotation caused by the ionosphere) and a summary of the results is shown in this paper.

ENVISAT ASAR is successfully operating since March 2002 and resulting ASAR products are operationally distributed to the user community since December 2002. This paper provides an update of the ASAR performance, from the instrument status to the product quality assessment.

Large differences are observed between radar backscatter measurements made by the ENVISAT and ERS-2 satellite synthetic aperture radars, within 30 min of each other over certain agricultural fields in Flevoland, The Netherlands. The differences appear to be caused by the presence of highly directive scattering combined with very small variations in the azimuth illumination angle of the two sensors at the degree or subdegree level. There is relatively little awareness of such sensitivity to illumination direction, and it is not predicted by models for microwave interaction usually applied to soils and vegetation. It is, however, to be expected if there are significant contributions from coherent scattering extending over patches of the agricultural fields in question. We present analysis that supports such a conclusion.

This document reports the analysis of various ALOS PALSAR products using the CALIX quality control tool and results from the verification campaign.

This document contains a list of quality control tools, which are intended to be used for ALOS PALSAR products verification and validation. The QC software tools are developed in two phases, i.e. the basic tools and the advanced tools. Input and output parameters are given, as well as a preliminary and survey-like description of the required algorithm steps. A short overview about the QC hardware tools is given as well.