Sentinel-5 Precursor (Sentinel-5P) is an Earth observation satellite created by the European Space Agency (ESA) as part of the Copernicus Programme. It was launched in October 2017 and is expected to last for 7 years. The satellite includes the Tropospheric Monitoring Instrument (Tropomi), which provides the most detailed monitoring of methane emissions available.
Overview
Sentinel-5P is the first mission of the Copernicus Programme focused on monitoring air pollution. Its instrument, Tropomi, is a special tool that measures light in different parts of the spectrum, including ultraviolet, visible, near-infrared, and short-wavelength infrared. The satellite is built on a hexagonal Astrobus L 250 satellite platform equipped with S- and X-band communication antennas, three foldable solar panels that generate 1500 watts of power, and hydrazine thrusters used to keep the satellite in the correct position.
The satellite operates in an 824 km (512 mi) Sun-synchronous orbit, passing over the same location on Earth at 1:30 PM local time each day.
The first major contract for Sentinel-5P was signed in July 2009 for the Tropomi instrument between the European Space Agency and the Dutch government, which contributed €78 million. On 8 December 2011, ESA chose Astrium UK as the main builder for the satellite, signing a contract worth €45.5 million. Construction of the satellite was completed in May 2014, followed by successful integration with its primary instrument. From design to launch, Tropomi cost €220 million.
The satellite was launched by Eurockot Launch Services using the Rokot rocket. The launch was originally planned for late 2014 but delayed several times. It launched on 13 October 2017 at 09:27 UTC from Plesetsk Cosmodrome Site 133. Sentinel-5P successfully reached its final orbit 79 minutes after launch.
Tropomi instrument
Sentinel-5P carries one instrument called the TROPOspheric Monitoring Instrument (Tropomi). Tropomi is a spectrometer that detects light in ultraviolet (UV), visible (VIS), near-infrared (NIR), and short-wave infrared (SWIR) wavelengths to monitor gases like ozone, methane, formaldehyde, aerosol, carbon monoxide, NO₂, and SO₂ in Earth's atmosphere. It improves on the abilities of the OMI instrument from the Aura satellite and the SCIAMACHY instrument from Envisat.
Tropomi takes measurements every second, covering an area about 2,600 km (1,600 mi) wide and 7 km (4.3 mi) in width, with a resolution of 7 x 7 km. The total weight of Tropomi is approximately 200 kg (440 lb), it uses about 170 watts of power on average, and it produces 140 gigabits of data per orbit.
Tropomi was built by a group of organizations including the Netherlands Space Office, Royal Netherlands Meteorological Institute, Netherlands Institute for Space Research, Netherlands Organisation for Applied Scientific Research, and Airbus Defence and Space Netherlands.
The instrument has four main parts: the UV, VIS, and NIR spectrometers and a calibration block; the SWIR spectrometer with its optics; the instrument control unit; and a cooling block. Light is separated into different wavelengths using grating spectrometers and measured by four detectors that match the specific light ranges. The UV spectrometer detects light from 270-320 nm, the visible light spectrometer detects 310-500 nm, the NIR spectrometer detects 675-775 nm, and the SWIR spectrometer detects 2305-2385 nm.
The SWIR spectrometer was designed and built by the Optical Payloads Group of Surrey Satellites (SSTL). It uses an immersed grating design where light hits an etched grating inside a high-index silicon material. This design allows for a compact and efficient structure. The SWIR grating was provided by SRON (Netherlands), who also supplied the Front-End Electronics (FEE). The SWIR spectrometer receives light from the main instrument through an intermediate pupil and directs it through a telescope to a slit that defines the instrument’s footprint on Earth. Light from the slit is re-collimated, diffracted by the immersed grating at high order, and then focused onto a two-dimensional detector by a high-aperture relay lens. The SWIR detector (supplied by Sofradir, France) has 256 elements across the track and 1024 elements in the spectral direction, with each element spaced 30 microns apart. It operates at a cold temperature (about 140 K). The SWIR spectrometer optics are mounted on a cooled optical bench (about 200 K) and insulated with a multiple-layer insulation (MLI) blanket. The SWIR instrument was aligned, focused, and tested at the Mullard Space Science Laboratory thermal vacuum facility in Surrey, UK.
Application examples
Satellite data from Sentinel-5P Tropomi showed large decreases in nitrogen dioxide levels above cities in China from late January to February 2020. These changes were connected to actions taken by China to address the coronavirus pandemic, which led to fewer industrial and polluting activities. Tropomi pollution data also supported a connection between higher numbers of COVID-19 cases and long-term exposure to air pollutants.