While originally designed to last only two years, SCISAT is set to celebrate its fifteenth birthday this August. The concept for the mission came about over 20 years ago and some of the data being collected is still unique. There’s no other satellite like it, and plans to replace it are in a bureaucratic holding pattern.
SCISAT simultaneously makes measurements of 66 trace gases in the atmosphere. “This is the most measured simultaneously from space and it’s done by Canadian instruments on a Canadian platform,” says Dr. Kaley Walker, SCISAT Deputy Mission Scientist and an atmospheric physicist at the University of Toronto.
The primary goal for SCISAT was to measure ozone depletion with a focus on Canada and the Arctic. Ozone is made up of three oxygen atoms and prevents most of Sun’s damaging ultraviolet radiation from reaching the Earth’s surface. Ozone is constantly created and destroyed through natural processes in the atmosphere and its amount changes depending on the how fast it gets created and destroyed.
One of its primary instruments is the Atmospheric Chemistry Experiment (ACE-FTS), a high spectral resolution infrared Fourier Transform Spectrometer. “You would find this instrument in chemistry laboratories. The one on the spacecraft is compact, but powerful. It looks at the Sun as the Sun rises or sets through the atmosphere,” says Mr. Thomas Piekutowski, the Sun-Earth System Sciences Program Manager at the Canadian Space Agency.
Most of these measurements by ACE are done through the solar occultation method, which takes measurements using the Sun’s rays as they pass through Earth’s atmosphere at sunrise and sunset. Since this satellite orbits the Earth every 90 minutes, it allows for approximately 6061 solar occultation measurements each year.
SCISAT spectra are done through limb-sounding, using a limb viewing geometry. “Limb-sounding is when you look at the atmosphere sideways, not straight down or up. It allows us to have very good vertical information, to see gases and aerosols at precise altitudes through the atmosphere,” says Mr. Piekutowski. Further to that, “half of the molecules measured by SCISAT aren’t measured with this vertical resolution by anyone else. There may be a total column measurement by looking down, which may only have sensitivity close to the ground or in the troposphere, but the vertical information that’s provided by SCISAT for the wide range of molecules is one of its strengths and what makes it unique. There’s nothing else in the pipeline at the moment,” says Dr. Walker.
The unique geometry of instruments on board SCISAT, the use of the Sun as a light source, and use of high spectral resolution allow the observation of a tremendous suite of species, unachievable by any other initiative.
A main factor contributing to the further destruction of ozone is industrial activities on Earth. In addition to observing the ozone content in the atmosphere, SCISAT looks at clouds and small particles, such as aerosols, to help scientists understand their effect on Earth’s climate. “The mission was very focused looking at ozone over Canada and in the Arctic. There was an eye towards the Montreal Protocol, but that came on stronger later. We got more into monitoring pollution and climate change and now we’re monitoring all of Montreal Protocol,” says Dr. Peter Bernath, research scientist at the University of Waterloo and SCISAT Mission Scientist who wrote the original proposal in 1998.
The Montreal Protocol is an international treaty to phase out the production of substances that contribute to the depletion of the Ozone layer. One of the biggest outcomes of this treaty has been the slow recovery of the ozone hole in Antarctica. “We are able to contribute to understanding the bigger questions relating to the Montreal Protocol in terms of looking at changes in chlorofluorocarbons, their breakdown products and reservoirs in the atmosphere. For example being able to verify yes, the amount of chlorine that causes human-caused ozone depletion is going down,” Dr. Walker told SpaceQ in an interview.
Chlorofluorocarbons (CFCs) are anthropogenic, human-made substances released to the atmosphere that destroy the ozone layer. Examples of where CFCs were used include: refrigerators, air-conditioners, aerosol cans, and insulating materials. CFCs were eventually phased out; their temporary replacements, Hydrochlorofluorocarbons (HCFCs), are now also phased out in developed countries but still being produced in developing countries. HCFCs will soon be completely phased out. “HCFCs will be replaced by other compounds because they have big climate effects. They want to phase them all out and we are monitoring about twenty or so of those molecules. We are literally monitoring the success of the Montreal Protocol,” Dr. Bernath told SpaceQ.
Water vapour is one of the main greenhouse gases that has a big effect on the climate. Data from SCISAT has shown that a previously observed increase in the stratosphere’s water vapour has stopped. Before SCISAT, the conventional wisdom was that Nitrous oxide (another main greenhouse gas) was primarily formed by micro-organisms on the surface. Nitrous oxide has a very long lifetime and makes its way to the stratosphere, making nitrogen dioxide in the end which destroys the ozone layer. “We discovered Nitrous oxide was also made by solar wind high in the atmosphere. In the winter when it gets cold and the air sinks over the poles, it can get down to the stratosphere and destroy some ozone,” says Dr. Bernath.
Understanding and studying Ozone depletion and climate change trends requires long-term, continuous datasets that can be analyzed. One of the most unique aspects of SCISAT is the longevity of the mission that has allowed for these trend analysis.
Other than shedding light on Ozone depletion and climate change factors, SCISAT has big implications for exoplanets. The Atmospheric Atlas produced from SCISAT data consists of some integrated Earth spectra. The occultation geometry of SCISAT used in its data collection is the same geometry used in transit spectroscopy. “Transit spectroscopy is where they look at the dip of the light when a planet transits in front of a star. Our atlas of the Earth, recorded in this occultation geometry, is exactly what an Earth-like planet would look like,” says Dr. Bernath.
The vast simultaneous measurement of molecules and their full long-term profiles are what make SCISAT unique. They not only allow scientists to observe what is happening in the atmosphere in a given time, but also helps in finding the cause of those changes.
Operations of SCISAT have been extended until March 2021. At that time, the health of the instruments and the quality of data will be examined in granting it another extension. When SpaceQ inquired on the original name of this mission, SCISAT-1, and whether there were plans for a SCISAT-2, Mr. Piekutowski said there are currently no plans for a follow-on mission.
“At the moment, there have been a number of missions that have been studies over the last 10+ years. The Chemical and Aerosol Sounding Satellite combines the strengths of ACE on SCISAT with some strengths of OSIRIS on ODIN mission. Unfortunately, we have gone through phase zero, but things have not gone further. There are lots of missions that seem to be in that position,” Dr. Walker told SpaceQ when inquiring about other follow-on missions.
“SCISAT cost about $64 million Canadian dollars at the time of launch. NASA gave CSA a free launch for SCISAT in return for all of Canada’s contribution to the International Space Station and the Shuttle program before that. Since launch, it has been costing around a couple of million dollars a year to run it, and we have been running it for about 15 years,” said Dr. Bernath. “For a small science mission that cost about $100 million in total we are competing against billion dollar European, American, and Japanese instruments; and there is still nothing like it out there.”
Archived video: In 2003 the Canadian SCISAT satellite was launched by Orbital using a Pegasus rocket. Credit AP.