Presentation on theme: "Satellite basics Estelle de Coning South African Weather Service"— Presentation transcript:
1 Satellite basics Estelle de Coning South African Weather Service Most slides taken from EUMETSAT training events, Jochen Kerkmann
2 CONTENT1. Introduction2. Satellite orbits3. Meteorological satellites4. The EM spectrum5. Satellite Image InterpretationVIS, IR, WV, 3.9 – 10.86. Summary
3 1. INTRODUCTIONRemote sensing is the science and art of acquiring information about an object, area or phenomena without actually being in contact with it.The sensor is usually mounted on moving platforms such as balloons, aircraft and satellites
4 1. INTRODUCTION (cont) Platforms of remote sensing are: Land based (surface or ground observation)Airborne based (from 100 m to 40 km)Space based (from 150 km to km)
5 2. SATELLITE ORBITS GEO LEO Located along the equatorial plane. About km above the earthHas Geo-synchronous orbitPeriod of 1436 minutesGood coverage from remote areasHas wide field of view ~ 50 degreesHas low resolutionProvides continuous data ~ min.Not very suitable for vertical soundingsNear polar orbitingkm above the earthHas Sun-synchronous orbitPeriod of 101 minutesExcellent coverage at the polesHas relatively narrow field of viewHas high resolutionPasses vary with latitudeVery suitable for vertical soundings
8 3. METEOROLOGICAL SATELLITES Many types of satellites have been launched for various purposes.For monitoring the environment, there are three types namely the:Meteorological (weather) satellitesEarth Resource satellites (ERS)Research and Development satellites (R&D).
9 4. THE EM SPECTRUM AND RESOLUTION The Electromagnetic (EM) spectrum is defined as a spectrum of all types of EM radiation in which each type of radiation is ordered according to its wavelength
10 Electromagnetic Spectrum The electromagnetic spectrum is a representation of the continuum of wavelengths, from long radio waves to the short x-rays and gamma rays. Note that the portion of the electromagnetic spectrum we can detect with our eyes (the visible portion) constitutes a very small portion of the electromagnetic spectrum.The microwave region (1mm-30cm) is also important in remote sensing of atmospheric temperature and moisture, as well as surface properties.
11 4. THE EM SPECTRUM (cont)In the visible portion features are observed by virtue of reflected solar energyIn the infrared portion, sensing of emitted energy predominatesRemote sensing data acquisition of surface features is limited to the non-blocked spectral regions of the EM referred to as atmospheric windowsAtmospheric windows define wavelength ranges in which the atmosphere is particularly transmissive of energy
12 7 MSG Window Channels Window Band (um) Airmass Band (um) VIS 0.6 WV 6.2VIS 0.8WV 7.3NIR 1.6IR 9.7MIR 3.9IR 13.4IR 8.7IR 10.8High Res VISIR 12.0HRV3 km data sampling intervals, except HRV (1 km)Images each 15 minutes (5 minutes Met-8 rapid scan)20/04/2017
13 4. THE EM SPECTRUM (cont)The atmospheric constituents like gases, aerosols and water vapour are selective absorbers of radiation depending on their wavelength, pressure and temperatureIn a clear atmosphere gas molecules such as carbon dioxide absorb radiation in selective wavebands creating a complicated pattern of atmospheric absorption bandsAn absorption band is defined as a range of wavelengths in the EM spectrum within which radiation is absorbed by a substance
14 4. THE EM SPECTRUM (cont) NON-ATMOSPHERIC WINDOWS Around 4.3 m, carbon-dioxideAround 6.7 m, water vapourAround 9.7 m, ozoneAround 15 m, carbon-dioxideAround 5 mm, oxygen
15 So much for very basic background information… Let us look at more practical examples of how to use satellite images…
18 5.1 VIS IMAGESLow clouds are less bright since they do not have large amount of ice. Their droplets contain more water that absorbs VIS rather than reflectHigh clouds consist of more ice crystals than water and are very brightClouds physical properties of high albedo are: large depth, high cloud water (ice) content, small average cloud-droplet sizeCloud physical properties of low albedo are: shallow depth, low cloud water (ice) content, large average cloud-droplet sizeVIS imagery shows shadows and helps to identify cloud structure when sun is at an angle.
20 5.2 IR IMAGESIR imagery indicates the Temperature of the radiating surface.Low cloud and fog can not be observed at night since their temperature is similar or near to that of surface.During the day such low clouds are detectable with VIS.Special properties of 3.9 micron radiation help in detecting low clouds at night
21 Channel 09 (IR10.8): Top Temperature Warm TopsMaputoCold TopsMSG-1, 6 November 2004, 12:00 UTC, Channel 09i (IR10.8i)Range: +50°C (black) to -70°C (white), Gamma = 1.0
22 Channel 09 (IR10.8): Top Temperature Warm TopsMaputoColdest TopsCold TopsMSG-1, 6 November 2004, 12:00 UTC, Channel 09 (IR10.8)
23 5.3 WV IMAGES (cont)Regions with high upper trop. Humidity appear white or light(cold) and regions with low humidity appears warm(dark)For moist atmosphere most WV radiation comes from middle layers.Very little moisture from lower layers is detected on the WV radiation.It is good tracer of atmospheric motionsCold and humidWarm and dry
24 Channel 05 (WV6.2): Upper Level Moisture High UTHMaputoLow UTHMSG-1, 6 November 2004, 12:00 UTC, Channel 05i (WV6.2i)Range: -20°C (black) to -70°C (white), Gamma = 1.0
26 MSG Channel Differences Useful to Monitor Convection
27 Difference IR3.9 - IR10.8: Cloud Particle Size MaputoLarge Ice Particles(+26/+35 K)Small Ice Particles(+65/+73 K)MSG-1, 6 November 2004, 12:00 UTC, Difference IR3.9 - IR10.8Range: -5 K (black) to +70 K (white), Gamma = 0.5
28 6. Summary VIS good for day time usage HRV to see fine-scale details IR108 good for vertical extent of clouds (Cloud top temp)WV6.2: shows high level moistureWV7.3 shows mid-level moisture (early convection)IR3.9 - IR10.8 best for particle size