Take a good look up at the sky. It may be gray with ominous clouds, or dark and starry with scattered white puffs. While clouds may not mean much to the average person, but for the scientists at NASA’s Goddard Space Flight Center in Greenbelt, Md., these clouds hold the answers to a mystery they have been working on since 2011. The Cloud-Aerosol Transport System (CATS), a remote sensing instrument known as a lidar, will provide critical information pertaining to the effect clouds have on Earth’s environment.
CATS will provide data about aerosols at various levels of the atmosphere. It will investigate the layers and composition of clouds and small particles like dust, smoke, and other atmospheric aerosols. The information collected can be used to improve the hazard-warning time before a natural disaster occurs. These events range from tracking plumes from dust storms to volcanic eruptions and wildfires. The information provided by CATS could also give scientists a better understanding of the effect clouds and aerosols have on Earth’s energy balance. The new technologies on CATS could potentially be used in future satellite missions.
Aerosols can be natural or man-made. They are tiny solid and liquid particles transported around the atmosphere and remain invisible to the naked eye. They include sea salt, smoke from fires, windblown desert dust, sulfurous particles from volcanic eruptions, and particles from fossil fuel combustion. They have been around humans forever in the form of fog, clouds, car exhaust, and even spray from a sneeze.
Scientists want to find how aerosols impact weather and climate. They are finding this to be a challenge because aerosols come in a variety of shapes, sizes, populations, masses, etc.
According to NASA, scientists get an understanding of clouds and air quality conditions in the atmosphere and generate air quality forecasts by combining high-tech computer models with satellite, aircraft, and ground-based data. Most of these datasets do not provide any details about the structure of layered clouds and aerosols.
“Clouds are one of the largest uncertainties in predicting climate change,” said Matt McGill, principal investigator and payload developer for CATS at Goddard. “For scientists to create more accurate models of Earth’s current and future climate, they’ll have to include more accurate representations of clouds.”
Clouds and aerosols soak in and cask back energy from the Sun in a rather complicated way. When the Sun’s energy reaches the top of the atmosphere, clouds are able to reflect incoming sunlight, which in return cools the Earth’s surface. On the contrary, clouds can absorb heat emitted by the Earth and then re-radiate it back down, heating the surface. The height, thickness, and structure of clouds in the atmosphere determine the amount of warming or cooling the Earth receives.
CATS is designed to operate for at least six months, with a goal of three years. The instrument will provide vertical profiles of cloud and aerosol properties at three wavelengths (1064, 532, and 355 nanometers). While on board the International Space Station, CATS will orbit between 375 kilometers (~230 miles) and 435 kilometers (~270 miles) above the Earth’s surface, at a 51-degree inclination with a three-day repeat cycle. CATS’s unique orbit will allow the instrument to observe the same area on Earth at various times every day.
According to the CATS Brochure, this will provide “far more comprehensive coverage of the tropics and mid-latitudes (between 51.6 degrees north and south latitude) than sun-synchronous orbiting satellites (like CALIPSO) that observe the same Earth scene at the same local time each day. This will allow scientists to, for the fist time ever, study the diurnal (day-to-night) changes in cloud and aerosol effects from space.”
The CATS Brochure provided on the CATS homepage provides details about the instrument and mission. There is a possibility that CATS could operate for as long as five years. This is pretty impressive considering that the instrument had to be designed and built in just two years and on a significantly smaller budget than traditional satellite missions.
Scientists are turning to active remote sensing instruments, like a lidar, to better observe the vertical structure of clouds and aerosols. Lidar works by utilizing a laser to submit a pulse of energy through the atmosphere toward a distant object. Once the energy reaches the object, some of the energy is cast back to the lidar receiver. The distance between the lidar and the object is calculated based on the time it takes the reflected energy to return to the receiver. The intensity of the return pulse allows scientists to infer other properties like the composition of clouds, the abundance of aerosols in the atmosphere, and the altitudes of cloud and aerosol layers.
NASA developed an airborne lidar system named the Cloud Physics Lidar (CPL) in 1999. Its primary purpose was to be used on the high-altitude ER-2 aircraft. The CPL uses a high-repetition-rate laser to provide atmospheric profile measurements of clouds and aerosols. The primary capability for CATS was adapted from this design.
In a July 2013 press release, NASA named two factors that make lasers essential to this kind of work. First of all, lasers emit on a very narrow wavelength that makes it simpler to measure changes caused by particles that reflect the incident light. Secondly, the light beam itself can be narrowly focused because the band is so narrow, like a needle poking tiny holes. CATS will be capable of detecting single photons returning from the scanned area.
The NASA CATS mission has three science goals:
- CATS will help extend the global lidar data record for continuity of climate observations. In particular, CATS will: continue the data record of vertical profiles of cloud/aerosol properties; improve our understating of aerosol and cloud properties and interactions; and improve model estimates of climate forcing and predictions of future climate change
- DATA from CATS will improve operational aerosol forecasting programs. In particular, the data will: improve model performance through assimilation of near-real-time cloud/aerosol data; enhance air quality monitoring and prediction capabilities by providing vertical profiles of pollutants; and improve strategic and hazard-warning capabilities of events in near real-time.
- The CATS payload will serve as a technology demonstration for future space-based lidar missions. In particular, the payload will: demonstrate High Spectral Resolution Lidar (HSRL) aerosol retrievals and 353 nanometer (ultraviolet) data for future mission development.
NASA’s CATS instrument is poised to launch on the fifth SpaceX cargo resupply mission (SpaceX CRS-5) to the International Space Station no earlier than 1:20 p.m. EST Friday, Dec. 19. Pre-launch news conferences will be held Thursday, Dec. 18, at NASA’s Kennedy Space Center in Florida. The final briefing at 3 p.m. will cover the CATS Earth science instrument headed to the space station.
– Follow our CRS-5 launch countdown and liftoff coverage for regular updates.
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