25 MAY 2020 



 8 JULY 2020 – 25 SEPTEMBER 2020 – 12:00 hrs noon (CEST) 

Submit your application for the TRUTHS Earth Watch Mission here –  [UPLOAD PERIOD ENDED]

In order to submit your application, you need to be a registered user. To register or to login to the site, please go to the Menu in the top left corner. Note the last uploaded version of your CV to this MAG membership application will replace any previously uploaded file version on this system, and will be used by ESA for membership evaluation


Membership of the TRUTHS EarthWatch Mission Advisory Group will be announced in Q4 2020.


Benchmark measurements of spectrally resolved Earth radiance and solar irradiance are key for robust, long-term monitoring of the global climate system. In the past decades, Earth observation satellite missions have been instrumental in identifying trends in solar, atmospheric, land, ocean and cryosphere parameters, allowing the separation and identification of climate change signals from natural variability. While this has been possible due to significant advances in science, instrumentation, calibration and processing, residual biases between missions and instrumental drifts remain limiting the capability to derive long- and short-term timeseries of critical climate variables.

The TRUTHS mission is designed to provide SI (System International) traceable fiducial reference measurements of the Earth radiation budget from near-UV to SWIR through direct observations establishing a ‘metrology laboratory in space’. TRUTHS main objective is to establish a reference (benchmark) measurement of the state of the planet, against which future observations can be compared, to:

1. allow climate model improvements and forecast testing; and

2. provide observational evidence of climate change including mitigation strategies in the shortest time possible.

Implemented as an Earth Watch mission, TRUTHS will provide essential data to a wide range of scientific and operational user communities, including climate modelers, NWP centres, essential climate variable (ECV) providers, space agencies and new space actors, aiming to reducing uncertainties in climate prediction for early decision making and improving satellite measurement through cross-calibration, with the two main applications:

  • Long-term reference benchmark datasets for monitoring climate change expressed through the Earth’s radiation balance with sufficiently low uncertainty (meeting GCOS requirements) to allow trends to be detected over approximately 15 years rather than 30+ years,
  • Operational products for removing biases in other satellite instruments by cross-calibration with TRUTHS data over a wide range of scene types and local cross-over times.

The current mission concept is based on a 3-axis agile satellite capable to point to the Earth and the sun in a reference non sun-synchronous low earth orbit at about 600 km altitude (to be confirmed). The operational mission lifetime is 5 years minimum, with a goal to launch in 2026.

The TRUTHS mission has the following three payloads:

  • Hyperspectral Imaging Spectrometer (HIS): Continuous spectral sampling across the nearUV-VIS-SWIR (320 nm to 2450 nm), 5-10nm spectral resolution, SNR 300, 50m spatial resolution, 50-100km swath, passively cooled @135K
  • Cryogenic Solar Absolute Radiometer(CSAR): On-board primary standard for radiance/irradiance, ~10 times more accurate than operational radiometers, actively cooled @60K
  • OBCS: On-Board Calibration System made of a Transfer Radiometer, low power Laser Diodes, Integrating Sphere and Wheel Diffuser with two diffusers.


TRUTHS Mission Terms of Reference

Scientific Readiness Levels Handbook

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