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About FSSCat

FSSCat was a ground-breaking mission concept that consisted of two federated 6U CubeSats, called ³Cat-5/A and ³Cat-5/B, which operated in support of the Copernicus Land and Marine Environment services. The mission concluded in 2021.

As a precursor to a constellation of federated small satellites for Earth Observation, FSSCat was equipped with a multi-spectral optical payload and a dual microwave payload, including a GNSS-Reflectometer and an L-band radiometer with interference detection/mitigation capabilities. FSSCat was capable of measuring soil moisture, ice extent, and ice thickness, and detecting melting ponds on ice. Additionally, the satellites featured radio/optical and Iridium inter-satellite links to evaluate key technologies and techniques for future satellite federations.

Mission Parameters
Date of launch3 September 2020
Mission StatusCompleted
Swath (across-track)300 km
Orbit Height540 km
Orbit TypeSun-synchronous
Orbit Period94 minutes

FSSCat Objectives

The primary objective of the FSSCat mission was to gather, in a cost-effective manner, data which supplemented the information provided by the Copernicus Sentinels, with a focus on supporting the Copernicus Land and Marine Environment services.

In achieving this goal, FSSCat aimed to deliver, via its optical and microwave payloads, data at a high temporal resolution with a moderate spatial resolution. Additionally, the mission aimed to demonstrate Inter-Satellite Links (ISL) through the use of its Laser Communication Payload.

FSSCat Instruments


FSSCat carried HyperScout-2 onboard which was a compact hyperspectral VNIR (Visible and Near Infrared) imager and multispectral (MS) Thermal Infrared (TIR) imager with a wide swath and powerful processing abilities. An artificial intelligence (AI) chip carried by the satellite allowed AI processing algorithms to be directly applied to acquired data while onboard, enabling the production of Level-1C hyperspectral data in-orbit.

AI was also leveraged to select which data was downloaded based on the cloud coverage of the acquired scene, an ability that was of particular benefit given the large volume of data generated by Earth observation hyperspectral imaging missions.

The microwave payload (FMPL-2) combined a GNSS-Reflectometer and an L-band Radiometer which performed sea-ice detection and thickness monitoring, and soil moisture measurements, which complemented data from HyperScout-2.

Characteristics of the L-1C VNIR TOA reflectance hyperspectral cube
AttributesHyperScout 2Justification
Field of view30° (ACT) x 15° (ALT)Based on on-ground characterisation
Orbit height540 kmBased on satellite ADCS
Swath Across track300 kmBased on instrument field of view and orbit altitude
Ground sampling distance GSD (Across track)75 mBased on instrument focal length and orbit altitude
Point Spread Function (PSF)2.0 px FWHM ACT 1.9 px FWHM ALTBased on on-ground characterisation
Active sensor size4000 x 1850 pxThe pixel dimension of the illuminated area of the sensor
Spectral Range450 - 950 nmAssuming there was sufficient band width to downlink the entire acquisition
Spectral Resolution18 nm FWHMBased on on-ground characterisation
Number of Bands50Depended on the acquisition scenario
Signal to noise ratio50Based on radiometric performance
Geometric accruacy~ 0.5 px average 0-3 pxBased on automatic keypoint comparison between HS and S2 imagery
Absolute Radiometric Accuracy10%Based on comparison with coregistered S2 bands
Bit Depth12Based on sensor and electronics design


The alignment accuracy of the data cubes was quantized using automatic keypoint detection methods provided by the OpenCV library. On average, the resulting interband accuracy was less than a half a pixel. However, because the georeferencing relied solely on visual data, the accuracy was generally lower on homogeneous landscapes where there were less distinct features to align on.

The radiometric accuracy of the HyperScout VNIR data was determined through comparison with Sentinel-2’s L-1C data products. The spectral bands of HyperScout were aggregated to match the band responses of Sentinel-2. To minimise the effect of co-registration errors and differences in contrast (MTF) on the validation of the radiometric quality, pixels binned to 10x10 tiles were compared.



ESA offers registered users access, through a dedicated FTP server, to the following data collection: