While today’s environmental satellites serve many important functions, one of the most critical is to provide meteorologists with data that are crucial to making accurate, life-saving weather predictions. These “eyes in the sky” constantly orbit above us. They make atmospheric observations that are ingested into numerical weather prediction (NWP) computer models and provide meteorologists with images of weather phenomena that allow them to monitor storms around the globe, identify volcanic ash and smoke from wildfires, and track hurricane development. For all of these reasons, the US National Oceanic and Atmospheric Administration (NOAA) has long recognized that environmental satellites are essential to meeting its mission to protect life and property, and why it will continue to maintain and improve this critical capability.
When the World Weather Watch (WWW) was established in 1963, however, environmental satellites were still in their infancy. Without the benefit of global coverage and near constant sampling of the Earth’s atmosphere, meteorologists relied on sporadic data from weather balloons, experience of past events, and reports from meteorologists closer to weather events of concern “upstream” from their location. Few observations existed across large expanses of the Earth’s oceans and sparsely populated regions, leaving meteorologists with little of the information they needed to make accurate forecasts. The five decades since 1963 have seen great advancements in the capabilities of environmental satellites, as well as in the abilities of the scientists to use them, and today we are on the cusp of an exciting new generation of environmental satellites.
In this article, we will first discuss the use of environmental satellites by meteorologists for weather forecasting, from both polar-orbiting and geostationary environmental satellites. Next, we will discuss the evolution of environmental satellites in the United States, from essentially a camera in space to today’s extremely capable sampling and imaging devices. Finally, we will conclude with a discussion of the next generation of US environmental satellites, and what these improvements will mean to meteorologists and the public they serve.
Weather forecasting with environmental satellites
Environmental satellites provide various types of data to meteorologists and are flown in different orbits in space. Below is a discussion of the types of data collected by environmental satellites, followed by an overview of the two principal orbits flown by environmental satellites and the capabilities provided by flying each.
Imaging and modelling
An obvious and unique capability of environmental satellites is their perspective – from space, satellites can see the Earth from afar, allowing meteorologists to watch storms and their development through the movement of clouds and water vapour. We refer to this capability as “imaging.” While imaging provides valuable information for all types of storms, this ability was extremely notable early in the development of environmental satellites for use in forecasting and monitoring hurricanes. Without it, prediction of powerful storms over the oceans was difficult, sometimes leading to disastrous outcomes. One well-known example, the 1900 Galveston Hurricane, struck residents in Galveston, Texas, without warning. Relying mainly on reports from land sources and a few ships at sea, forecasters in Galveston had little ability to know its precise location in the Gulf of Mexico or to accurately predict its future movement in order to warn residents. Thus, the powerful Galveston Hurricane caused an estimated 8 000 deaths, making it the deadliest hurricane in US history.
Imagery is not the only valuable capability provided by environmental satellites. Satellites are vital to the operation of NWP models, which need atmospheric observational data to function. NWP models, such as the US Global Forecast System (GFS) or the European Centre for Medium-Range Weather Forecasts (ECMWF) model, take these atmospheric data, create a snapshot of the current atmosphere, and run highly complex calculations to predict what the atmosphere will do next. Meteorologists then use the NWP model outputs, called “forecast guidance,” to help aid them in preparing their weather forecasts. This approach has revolutionized weather forecasting, resulting in dramatic improvements in forecasting accuracy.
To be effective, NWP models require an accurate understanding of the current state of the atmosphere, including its temperature, pressure and water vapour at different levels of the atmosphere and from around the Earth. Polar-orbiting environmental satellites from NOAA and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), with their ability to rapidly sample the atmosphere around the entire globe, are the primary data sources used by these NWP models and are critical to their forecast accuracy at three days and beyond. “Sounders,” a type of radiometer instrument flown on these satellites, are able to provide the vertical profiles of temperature, pressure, and water vapour needed by NWP models. While other critical sounding data come from weather balloons and other sources, nothing is able to match the ability of environmental satellites to provide an accurate and complete sampling of the Earth’s entire atmosphere and ocean temperatures.
Polar-orbiting and geostationary satellites
Polar-orbiting satellites orbit the Earth at just over 800 km above the surface, circling over the North and South Poles approximately every 100 minutes. With the Earth spinning beneath these low altitude satellites, the satellites cover a different strip of its surface in each orbit, eventually sampling the entire planet. While these satellites also provide imagery, their sounders produce highly accurate profiles of the Earth’s atmosphere and ocean temperatures that are ingested into NWP models.
Geostationary satellites orbit the Earth at over 35 000 km above the Equator, spinning at the same speed as the Earth. This allows them to appear to hover over the same portion of the Earth and to provide constant monitoring of rapidly developing weather. These geostationary satellites are principally used to provide images of the Earth, which when looped together, allow meteorologists and the public to see the growth and movement of clouds and storms in the atmosphere. This information is especially critical for short-term forecasting, or nowcasting, of severe weather.
Brief history of environmental satellites
The first image broadcast from TIROS-1 the first US environmental satellite in 1960.
On 1 April 1960, the US launched the world’s first weather satellite: the Television Infrared Observation Satellite-1 (TIROS-1). This satellite weighed only 122.5 Kg, and carried two cameras and two video recorders. While it only flew for 78 days, the images it beamed back to Earth proved that satellites could play a useful role in weather forecasting. TIROS-1, along with other early TIROS satellites, demonstrated the utility of satellites for weather forecasting and helped garner support for new launches and continued operation of environmental satellites for weather forecasting.
New generations of polar-orbiting satellites, each with important technological advancements, continued to be developed and launched after those early missions. In 1978, an important new generation of polar-orbiting satellites was launched, the Advanced TIROS-N series, followed in 1998 by the latest generation of polar-orbiting environmental satellites, now called Polar-orbiting Operational Environmental Satellites (POES). In addition to flying sounders and imagers, POES satellites are also part of the international Search and Rescue Satellite-Aided Tracking system, or SARSAT, and fly special, internationally-provided instruments that detect the location of distress signals from emergency beacons on planes, ships and boats, and stranded hikers. In 2012, more than 250 rescues benefited from the help of SARSAT. The last POES satellite, known as NOAA-19, was launched in February 2009 and continues to provide crucial data to NWP models.
The NOAA/NASA4 Suomi National Polar-orbiting Partnership (Suomi NPP) mission, launched on 22 October 2011, is a bridge between NOAA’s POES spacecraft (and NASA’s legacy Earth observing missions) and NOAA’s next-generation Joint Polar Satellite System (JPSS). As Suomi NPP is the first to fly the groundbreaking new instruments that JPSS will use operationally, it will be addressed in greater detail in the discussion of the next generation of environmental satellites.
On 6 December 1966, the US launched the first environmental satellite to geostationary orbit: the Applications Technology Satellite-1 (ATS-1). The spin scan cloud camera on ATS-1 produced visible images of the Earth every 20 minutes, and because the satellite was stationary with respect to the Earth’s surface and could see such a large amount of its surface, sequencing these images allowed scientists to track the large-scale movements of clouds. Additional ATS satellites were launched through the mid-1970s, each demonstrating new instrument technologies. The series culminated with ATS-6, the first geostationary weather satellite to be stabilized, instead of spinning like a top. This advancement allowed ATS-6 to view the Earth’s surface constantly, rather than only when the spinning instrument was facing Earth.
In the early 1970s, meteorologists began using imagery from ATS satellites. Following the success of this use, NOAA and its close partner, NASA, began developing the Geostationary Operational Environmental Satellite (GOES) programme to create an operational geostationary satellite programme. GOES-1 was launched in 1975, and it also included a radiometer that allowed for day and night observations. GOES-2, launched in 1977, allowed NOAA to achieve the two-satellite constellation in geostationary orbit that it still uses today – with one GOES satellite serving as GOES-East, covering the eastern half of the US and most of the Atlantic Ocean, and the second GOES satellite operating as GOES-West, covering the western half of the US and much of the Pacific Ocean and Hawaii. Today, GOES-13, launched in 2006, operates as GOES-East, and GOES-15, launched in 2010, operates as GOES-West. NOAA keeps a spare geostationary satellite in orbit over the central US, which today is GOES-14, which can be activated if one of the operational GOES experiences trouble.
January 2011 snowstorm, one of the three types of images provided by GOES satellites
A bright future for environmental satellites
While the five decades since the establishment of the WWW have seen incredible advances in environmental satellites and their use, we are entering an exciting age of more capable and advanced environmental satellites that will provide meteorologists in the US and around the world with the tools they need to do their job more effectively. Here is a look at the next generation of both polar-orbiting and geostationary environmental satellites.
Suomi NPP and the Joint Polar Satellite System (JPSS)
As mentioned before, the successful launch of a new polar-orbiting environmental satellite on 28 October 2011, Suomi NPP, created a bridge between NOAA’s POES (along with NASA’s Earth observing missions) and the next generation of polar-orbiting environmental satellites, the Joint Polar Satellite System (JPSS). Suomi NPP, which weighs about 2 000 kg and is the size of a large van, is being used operationally by NOAA to continue issuing accurate forecasts and advance warnings for severe weather such as deadly tornado outbreaks and floods, blistering heat waves, paralyzing snowfall, and raging wildfires.
A “full disk” image (as opposed to a zoomed-in image) from the GOES-East satellite.
Nearly all of Suomi NPP’s instruments are more advanced versions of those flown on POES satellites, which were designed using technology developed in the late 1980s to early 1990s. The five key instruments include two sounders, the Advanced Technology Microwave Sounder (ATMS) and Cross-track Infrared Sounder (CrIS), along with the Visible Infrared Imaging Radiometer Suite (VIIRS), Ozone Mapping and Profiler Suite (OMPS), and Clouds and the Earth’s Radiant Energy System (CERES). NOAA feeds data collected from these instruments into NWP models and uses the data to generate dozens of additional products, including measurements of clouds, vegetation, ocean colour, and land and sea surface temperatures.
|Suomi NPPimage of Hurricane Sandy taken at night, showing city lights and the clouds of Sandy lit by moonlight||Infrared image of Sandy from Suomi NPP|
NOAA and NASA are using the lessons learned from Suomi NPP as they build and prepare for JPSS-1. The instruments flown on Suomi NPP will also be flown on JPSS-1, which is scheduled for launch in 2017. We are just beginning to see the benefits and new uses of these data, and from what we have already seen, the JPSS programme is expected to bring huge benefits to meteorologists and to the societies they serve.
The first image produced by the Suomi NPP visible imager instrument, showing the swath of Earth visible in each pass of a polar-orbiting satellite.
NOAA and NASA, as partners, are also developing the next generation GOES satellites, the GOES-R Series. The first of these advanced geostationary environmental satellites is scheduled for launch in late 2015. These satellites promise to have four times the clarity of current GOES satellites and to provide more than 20 times the amount of data. The GOES-R Series will consist of four satellites – GOES-R, -S, -T, and –U, which will extend the GOES operational lifetime through to at least 2036.
The GOES-R Series will usher in a new era for geostationary environmental satellites, providing continuous imagery and atmospheric measurements of the Earth’s Western Hemisphere. GOES-R’s improved instruments, primarily its Advanced Baseline Imager (ABI), will provide significant advances in imaging capabilities that will provide three times more spectral information, four times the spatial coverage, and five times the temporal resolution compared to the current GOES imagers. A new Geostationary Lightning Mapper instrument will allow continuous and near real-time surveillance of total lightning activity from the middle of the Pacific Ocean to the middle of the Atlantic. Additionally, the GOES-R Series will provide significant enhancements in solar monitoring and space weather forecasting.
From tracking hurricanes in the Atlantic Ocean to severe weather in the Great Plains of the central US, the GOES-R series of geostationary environmental satellites represents a significant improvement over the current capabilities of NOAA’s geostationary satellites. GOES-R, together with the improvements in polar-orbiting satellite capability brought by Suomi NPP and JPSS, will provide noticeable improvements to meteorologists and those that rely on their forecasts.
Other environmental satellites
In addition to the traditional polar-orbiting and geostationary environmental satellite missions, the future promises to bring advancements from new types of environmental satellite data. Many exciting satellites are already in orbit, and scientists and meteorologists are learning new ways to incorporate their data into forecasts.
One notable example is the Jason series of satellites. Principally a sea surface topography mission, Jason-2 is an international mission that flies an altimeter that provides high-precision measurements of sea surface height. Because the temperature of the ocean and ocean currents can change the height of the sea and these characteristics can affect the world’s weather, including tropical storms, Jason-2 has been crucial to improvements in weather modeling and tropical storm intensification forecasting. Its follow-on, Jason-3, is currently under development.
An additional example is the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC), an international mission that uses six micro satellites equipped with advanced GPS radio occultation receivers. By measuring deviations of GPS signals caused by temperature and moisture gradients in the atmosphere, data from these satellites are able to provide very accurate vertical profiles of temperature and moisture. When ingested into NWP models, this additional data has proven capable of improving model accuracy.
Improved satellites and weather forecasts
Since the founding of the WWW, we have come a long way in weather forecasting. Increases in computing power, improvements in communications and the development of NWP models have all changed the way meteorologists practice their craft. However, perhaps no change has had as big of an impact on weather prediction as the invention and improvement of environmental satellites.
Since environmental satellites first flew over 50 years ago, vast improvements in their reliability, coverage and capabilities have enhanced understanding of the composition of the atmosphere in real time and the tracking of severe weather in ways once thought impossible. Important international collaboration in environmental satellites, with partners in Europe, Asia and other continents, continue the long tradition of international collaboration in weather observations and has allowed these improvements to benefit societies around the world.
And thankfully, the future of environmental satellites looks promising. While fiscal difficulties have impacted many governments and present real challenges to the ability to prevent gaps in critical satellite coverage, the United States and other nations have not questioned the need to maintain the environmental satellite coverage critical to weather forecasting and the protection of life and property. NOAA’s next generation of environmental satellites, JPSS and GOES-R, together with the use of new forms of satellite technology, promise continued advancements in the capabilities of environmental satellites for the decades to come and improved weather forecasts for the public.