Professional Pilot, January 2019

Satellite weather Visual satellite image of a winter storm departing the eastern US in January 2016 High resolution visible imagery regions of adverse weather but are limited to daytime hours as they rely on light A s the pilot wrestled the yoke against the incessant moderate turbulence among the towering convective cells that had popped up seemingly all around them the copilot was using his electronic fl ight bag to access the most recent weather information Sure enough a convective sigmet had been issued for a pretty large area through which they were now fl ying With tops above FL400 it seemed unlikely that theyd be able to climb above things But when he tapped the link to the latest visual satellite image he saw that a large section of the sigmet region off to their left was devoid of the cloud deck that was plaguing them at the moment Informing the pilot that clear air could be found just about 20 miles to the left the crew requested a deviation from their route and within a few minutes had broken out into clear air Using the satellite image they plotted a VMC route around the adverse weather Eyes in the sky For the fi rst 50 years or so of fl ight pilots relied solely on what they could see along with weather reports from airports 80 PROFESSIONAL PILOT January 2019 can help pilots easily distinguish cloud types and along their routes or pilots fl ying ahead of them If they were fortunate they might have access to rudimentary weather maps that gave them some clue about the bigger weather picture But that changed in February 1959 with the launch of the Vanguard 2 weather satellite Though its images were of little use due to technical problems Vanguard 2 demonstrated the possibilities of satellite weather observation and by 1960 TIROS 1 and then the Nimbus series of weather satellites were forever changing the way pilots and meteorologists saw the atmosphere At that point a single image beamed down from space could display cloud patterns and other measurements over a large area and though it would take many more years that image would eventually become accessible to pilots for fl ight planning and routing Interestingly while Vanguard 2 yielded disappointing imagery of the cloud cover it was intended to observe it remains in orbit to this day along with its 5 successor Vanguard satellites still providing valuable telemetry data and information about the density of the upper atmosphere At present there are at least 25 primary weather satellites in orbit Given the expense a single weather satellite may cost upward of 1 billion dollars it is no surprise that these satellites are launched and maintained by the governments of the worlds largest economies United States Japan China Russia the EU and India This constellation of satellites however provides near complete global coverage of the atmosphere At any given moment terabytes of data are fl owing toward receiving stations and being processed into hundreds of graphical depictions of different aspects of the weather we will face as we launch ourselves into the sky The weather satellite constellation is divided into 2 primary types geostationary and polar orbiting both having advantages and disadvantages for pilots Geostationary satellites orbit high above the earth at an altitude of around 22300 miles 36000 km in order to not only maintain an orbit speed that matches the speed of earths rotation but to also capture a wide angle image of a large part of the planet over which they are positioned Some cameras are even able to see the fulldisk of the entire planet As the name implies geostationary satellites orbit in such a way that they remain above a fi xed spot on earth at some location along the equator The advantage of this is that the satellite can perpetually observe the same geography giving the ability to track the movement of the weather over time Simply comparing one image to the next can reveal how quickly a weather system may be evolving or moving across the landscape A downside of a geostationary satellite is that what it provides in spatial coverage it loses in detail Digital cameras can only see at a given pixel resolution The farther the camera is from its subject the larger is the area included in that single pixel Additionally because of their fi xed position the camera cannot see the entire planet and the part it can see goes through daily phases of light and dark The other orbit is polar orbiting also called low earth orbiting These satellites orbit over the poles at an altitude of about 530 miles 850 km while the earth rotates beneath them This confi guration allows the satellites not only to scan a smaller swath of earth with great resolution but also to make a complete scan of the earth every 24 hours This is useful for a variety of applications and for aviation is important to capture what may be happening along polar routes Of course the downside is that except where the swaths overlap at higher latitudes and the poles a location may only be scanned once per day These satellites therefore are limited in their usefulness for tracking fast moving weather systems WEATHER BRIEF Photographs from space can paint useful pictures for pilots By Karsten Shein Comm Inst Climate Scientist Image courtesy NASA