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Chapter III: Satellites and orbits

Satellites and orbits

Meteorological instruments are flying on satellites in different orbits around the Earth. The choice of the orbit mainly affects the frequency a particular spot on earth is continuously scanned by the instrument (timely resolution). The height of the orbit has only a minor influence on spatial resolution, this depends much more on the instrument type and the viewing geometry.

Because of the viewing geometry, most atmospheric sounding instruments will be found on low earth orbiting (LEO) satellites (e.g. vertical temperature and moisture sounding instruments, ASCAT, sea level altimeter, microwave sounder, etc.), but also because active instruments need to be close to the measuring object.

Satellites in a geostationary orbit (GEO) have an orbital period same as the Earth's rotation period. This allows for scanning the earth atmosphere from a fixed viewing perspective. Passive sounding instruments will be found more and more on GEO satellites in the future (e.g. GOES and MTG).

Training resources of the first chapter will deal with the satellite orbits and the last 2 chapter provide an overview on current European and non-European satellites.


Satellites and Orbits: From Past to Current Satellites (Webcast, 30 minutes), 2014

The invention of weather satellites has opened a new area in weather forecasting. Satellite observations enable to continuously monitor the weather regimes on the whole globe. Therefore, they provide a powerful tool in weather forecasting. This lecture leads from the invention of weather satellites to the current operational satellites.

Satellite Orbits (Webcast, 60 minutes), 2011

Satellite orbits depend on the flying height of the satellites. This height is defined by gravitational and centrifugal forces. Geostationary satellites operate in a height of about 36000 km and provide high temporal resolution. In contrast polar satellites are found closer to the surface and therefore offer higher spatial resolution. The second lecture of the satellite course leads from the physical principals to benefits and limitations of selected satellite orbits.

European satellites

Introduction to MTG (Webcast, 30 minutes), 2016

Jochen Grandell starts his presentation by introducing the Meteosat program from the beginning. Then he explains what the MTG mission is and what kind of instruments will be on-board the MTG satellites. He introduces the Flexible Combined Imager (FCI) and the Lightning Imager (LI). The differences between SEVIRI on-board MSG and FCI are discussed in more detail. The measurement technique of the LI is shown together with the role of this very new instrument.

Anticipated benefits of improved temporal and spatial resolution (Webcast, 35 minutes), 2016

The presentation addresses some of the general impacts of the higher temporal and spatial resolution, available with the most recent or upcoming geostationary weather satellites. Main contribution of the higher scan frequency (of the order of 2.5 minutes or shorter) is in much better temporal coverage of evolution of rapidly developing weather systems, namely those associated with deep convection. The impact of shorter scan frequency will be demonstrated using data from the MSG 2.5-minute experiment. Spatial resolution affects not only the fidelity of imagery, but also (and more importantly) some of the quantitative characteristics of cloud tops - such as local cloud top brightness temperature minima, associated with overshooting tops. This effect will be demonstrated using high resolution polar satellite imagery.

Geostationary Satellites (Webcast, 42 minutes), 2011

Geostationary satellites enable to closely monitor the weather development at selected locations. This is particularly important for nowcasting convection and high impact weather. This lecture leads from general advantages of geostationary satellites to specific applications.

Polar Orbiting Satellites (Webcast, 60 minutes), 2011

Polar orbiting satellites fly at relatively low altitudes of about 800 km above Earth. Therefore, they can provide satellite images at high horizontal resolution. When only one polar satellite is employed, the same spot on Earth is visited only twice per day. Therefore, more than one polar satellite with different equatorial crossing times is required in order to attain more frequent observations. This lecture introduces you with the different instruments onboard of MetOp A and gives insight into the application of the retrieved information.

Non-European satellites

An overview of Himawari-8/9 (Webcast, 30 minutes), 2016

The new-generation geostationary meteorological satellite of the Japan Meteorological Agency (JMA), Himawari-8, started operation in July 2015. Himawari-8 features a new imager, Advanced Himawari Imager (AHI), with 16 bands. The imager's spatial resolution and observation frequency is improved comparing with its predecessor satellites, MTSAT-series. This presentation will be an overview of Himawari-8/9. It will focus on the imaging capabilities and the data distributions.

NOAA's Preparations for the Next Generation of Geostationary Satellite: GOES-R (Webcast, 30 minutes), 2016

The next generation of geostationary satellite, GOES-R, was launched in November, 2016 And GOES-S in March 2018. NOAA has been preparing for the data from its Advanced Baseline Imager and Geostationary Lightning Mapper for the near future, . JMA launched Himawari-8 and -9, a geostationary satellite with a similar imaging instrument. This presentation will show how Himawari-8 data has been used to prepare for similar data to begin flowing in early 2017. Meteosat Third Generation (MTG) will also carry a similar imager, so lessons learned from Himawari and GOES-R and S will be helpful for MTG data users.

Entering the GPM constellation and Megha-Tropiques era (Webcast, 47 minutes), 2015

In this lecture, I will focus on the rainfall in the tropical regions and I will present the multi-platforms precipitation products that are available. I will explain the functioning of the retrievals and will put the emphasis on the characterisation of the errors and uncertainties associated with the satellite products. Time will be devoted to the introduction of the passive microwave Global Precipitation Measurements constellation with emphasis on the Megha-Tropiques mission. An effort will be made to showcase what the end user can expect from the products developed in many centers worldwide with examples from various validation campaigns. I will end the lecture with a brief presentation of the activity and available resources of the International Precipitation Working Group from WMO/CGMS.

Global Precipitation Measurements for Science and Society (Webcast, 45 minutes), 2015

The Global Precipitation Measurement (GPM) mission is an international network of satellites that provide next-generation global observations of rain and snow. The GPM concept centers on the deployment of a GPM Core Observatory satellite (launched Feb 2014), which is a joint NASA/JAXA partnership. The GPM Core Observatory operates an advanced radar and radiometer system to measure precipitation from space and serves as a reference standard to unify precipitation measurements from a constellation of research and operational satellites. GPM has a unique role in providing datasets for science and societal applications related to the Earth's water cycle at both regional and global scales and over long time periods if one includes the 17-year record of precipitation from the Tropical Rainfall Measuring Mission (TRMM) along with the expected 10 years from GPM. GPM is a mission with both scientific and application goals and as such has both high-quality research data products and near real-time (NRT) data products. The NRT products are released 1-6 hours after data collection and are important for operational users and weather-related disaster applications. Some products are every 30 minutes and at a 0.1deg by 0.1deg (~10km by 10km) footprint. The research products are used for scientific research and climatology and weather/climate models. During this lecture information will be presented on how the satellite instruments work, the retrievals algorithms perform, the data is used for scientific investigations and societal applications such as floods, landslides, cyclones, and how to obtain GPM datasets.