No Paraskevidekatriaphobia For Sentinel-5P!

Sentinel-5P carries the state-of-the-art Tropomi instrument. Image courtesy of ESA/ATG medialab.

On Friday the latest of the Sentinel satellites, Sentinel-5P, is due to be launched at 09.27 GMT from Plesetsk Cosmodrome in Russia.

Friday is the 13th October, and within parts of the western world this is considered to be an unlucky date – although in Italy its Friday 17th which is unlucky and in some Spanish speaking countries it is Tuesday the 13th. Fear of Friday 13th is known as paraskevidekatriaphobia, although evidently it isn’t something Sentinel-5P worries about!

Sentinel-5 Precursor, to give the full title, is dedicated to monitoring our atmosphere. It will create maps of the various trace gases such as nitrogen dioxide, ozone, formaldehyde, sulphur dioxide, methane and carbon monoxide alongside aerosols in our atmosphere. The mission will also support the monitoring of air pollution over cities, volcanic ash, stratospheric ozone and surface UV radiation.

An internal view of the Copernicus Sentinel-5P satellite. Image courtesy of ESA/ATG medialab.

The satellite itself is a hexagonal structure as can be seen in the image to the right. It has three solar wings which will be deployed once the polar sun-synchronous 824 km low earth orbit has been achieved. Sentinel-5P will be orbiting three and half minutes behind NOAA’s Suomi-NPP satellite which carries the Visible/Infrared Imager and Radiometer Suite (VIIRS). This synergy will allow the high resolution cloud mask from VIIRS to be used within the calculations for methane from Sentinel-5P.

Within the hexagonal body the main scientific instrument is the Tropospheric Monitoring Instrument (Tropomi). This is a push-broom imaging spectrometer covering a spectral range from ultraviolet and visible (270–495 nm), near infrared (675–775 nm) and shortwave infrared (2305–2385 nm). The spatial resolution of the instrument will be 7 km x 3.5 km. However, one of the exciting elements of this instrument is that it will have a swath width of 2600 km meaning it can map almost the entire planet every day. It will have full daily surface coverage of radiance and reflectance measurements for latitudes > 7° and < -7°, and better than 95 % coverage for other latitudes.

The key role of Sentinel-5P is to reduce the data gap between the end of the Envisat mission in May 2012 and the launch of Sentinel-5 in 2020. Sentinel-5, and Sentinel-4, will be instruments onboard meteorological satellites operated by Eumetsat and both will be used to monitor the atmosphere.

The timing of Sentinel-5 is interesting for those of within the UK given that almost three quarters of the funding from Copernicus comes from the European Union. By this time Brexit will have occurred and it is currently unclear how that will impact on our future involvement in this programme. This also applies to the work announced at the end of last month to look at an expansion of the Sentinel missions. Invitations to tender (ITT) are due to be issued in the near future, and given our previous blogs on potential limitations and issues, it will be interesting to see which UK companies bid, and whether they will be successful.

Sentinel-5P will help improve our understanding of the processes within the atmosphere which affect our climate, the air we breathe and ultimately the health of everyone on the planet.

Did you know remote sensing goes extra-terrestrial?

Ceres captured by NASA's Dawn spacecraft on 19 Feb 2015. Image courtesy NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Ceres captured by NASA’s Dawn spacecraft on 19 Feb 2015.
Image courtesy NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

If you didn’t realise remote sensing of other planets and space objects occurs, you’re not alone. Remote sensing is playing an important role in helping us understand how our planet, and our universe, was created; however this isn’t celebrated much outside, or even within, the remote sensing community. We discussed this topic when ESA’s Rosetta arrived at Comet 67P, and it surfaced again last week when NASA’s Dawn spacecraft went into orbit around the dwarf planet, Ceres, which lies 38 000 miles away, between Mars and Jupiter.

Dawn’s mission is to study Ceres and the asteroid Vesta, which it orbited during 2011 and 2012, to develop our understanding of early solar system formation. There was a lot of media attention about Dawn’s arrival at Ceres, as it’s the first spacecraft to visit a dwarf planet and also the first to orbit two different non-earth objects. The technical and engineering feat to get Dawn to Vesta and Ceres is amazing, but the science to acquire, and interpret, the data is pure remote sensing. However, you rarely see it described as such within the headlines.

Dawn carries three scientific instruments:

  1. A camera, designed by the Max Planck Institute for Solar System Research in Germany, which will provide both three colour and panchromatic images, and when it descends into a low orbit around Ceres it will offer 62m spatial resolution. It can use 7 different colour filters, detect near-infrared energy and has an 8 gigabyte internal memory. As the camera is vital to both the navigation, and the science, side of the mission, Dawn carries two identical, but physically separate, versions.
  2. A Visible and Infrared Mapping Spectrometer (VIR-MS) designed and built by Galileo Avionica in Italy to provide surface maps. The instrument has a high spectral resolution of between 0.25 – 1µm in the visible light range, and 0.95 – 5µm in infrared, and has 6 gigabits of internal memory. Interestingly, it was based on the VIRTIS instrument carried by Rosetta to map Comet 67P.
  3. Gamma Ray and Neutron Detector (GRaND) — The instrument has 21 sensors, a wide field of view and produces maps of Ceres measuring the rock forming elements, trace elements, radioactive elements as well as Hydrogen, Carbon and Nitrogen. It was developed by the Los Alamos National Laboratory in the United States, and unlike the other two instruments has no internal storage.

Supporting these instrument measurements will be various radiometric and navigational data to help determine the gravitational field. The fundamental principles of remote sensing – measuring the reflected energy of the planet to determine what is on the surface – is right at the heart of Dawn’s mission. So why isn’t the remote sensing community shouting more about it?

We’re probably as guilty as everyone else here; we refer to Pixalytics as either a remote sensing company and/or an Earth observation company. Is it this association to Earth, which means we don’t always acknowledge the work, and achievements, beyond our planet?

Remote sensing is leading the way in enhancing knowledge about how the universe began; this is our scientific field that is helping make this possible. So let’s make some noise for the remote sensing community, elbow the space engineers out of the way to get ourselves into the news and let everybody else know what remote sensing can do!

Rosetta: Extra-terrestrial Observation

Full-frame NAVCAM image taken on 9 August 2014 from a distance of about 99 km from comet 67P/Churyumov-Gerasimenko. Image: ESA/Rosetta/NAVCAM

Full-frame NAVCAM image taken on 9 August 2014 from a distance of about 99 km from comet 67P/Churyumov-Gerasimenko. Image: ESA/Rosetta/NAVCAM

Most people will have seen last week’s news about ESA’s Rosetta spacecraft arriving at comet 67P/Churyumov-Gerasimenko and the animated images of the ‘rubber-duck’ shaped object taken from Navigation Camera (NavCam), part of Rosetta’s Attitude and Orbital Control System. The arrival generated many headlines, from the 10 years it took to catch the comet, through the history making first rendezvous and comet orbit, to the final part of the mission and the intention to land on the comet. However there was little detail about the remote sensing aspect of the mission, which we feel is a missed opportunity as it’s using many of the techniques and methodologies employed in Earth observation (EO).

The orbiter part of Rosetta carries eleven different remote sensing experiments with a wide variety of sensors gathering data about the comet before the lander touches down. Amongst the instruments on-board are three separate spectrometers; a visible and infrared thermal imaging spectrometer (VIRTIS) focussing on temperature and geography; an ultraviolet imaging spectrometer (ALICE) looking at gases and the production of water and carbon dioxide/monoxide; and finally ROSINA has sensors for measuring the composition of the comet’s atmosphere and ionosphere.

The VIRTIS instrument has two channels; the VIRTIS-H channel is a high spectral resolution mapper operating from 2 to 5µm, whereas the VIRTIS-M is the mapper operates at a coarser spectral resolution and one of its main products will be a global spectral map of the comet’s nucleus. This instrument has already been used to undertake measurements of Earth. In November 2009, on Rosetta’s third Earth fly-by, VIRTIS measurements were compared to existing EO instruments from ENVISAT/AATSR, SCIAMACHY and MODIS. Overall, there was a strong correlation with the EO data, but differences were also seen – especially in the 1.4µm water absorption feature.

VIRTIS has a key role in supporting the selection of the November’ landing site, a task that has become more difficult now the comet has been imaged in detail and is seen to have a complex shape. In addition, recent VIRTIS measurements have shown the comet’s average surface temperature to be around minus seventy degrees centigrade, which means the comet is likely to be too warm to be ice covered and instead must have a dark, dusty crust.

Remote sensing is playing a huge part in the Rosetta mission and it should be celebrated that these instruments will gather data over the next eighteen months to help scientists determine the role comets play in the evolution of planets. It will be amazing if remote sensing techniques developed to explore, monitor and analyse our planet, will be the same techniques that help determine if the water on Earth originally came from comets.