Basics of Satellite Imagery Analysis VS 03UTC, 8 July 2015 29 June 2016 Japan Meteorological Agency Basics of Satellite Imagery Analysis Basics of satellite imagery Review of radiation physics Features of each channel VS IR, I2 WV I4 S1 (IR-I2), S2 (I4-IR) Meteorological Satellite Observation of infrared and reflected solar radiation from the Earth and its atmosphere Provision of data on atmospheric/cloud movement Useful especially for analysis of weather phenomena at sea Very important for identification of TS areas 1978 GMS (JMA) Global Observing System in 2025 4 wikipedia Satellite Orbits Geostationary Satellite The geostationary satellite orbits in line with the earth’s rotation, so remains over the same spot on the earth. It is positioned at approximately 35,800 km above the equator. It conducts ongoing observation over a large fixed area (1/3 of the Earth). It provides data with high temporal resolution. Due to the satellite’s high orbit, the spatial resolution of its data is limited. Satellite Orbits Polar-Orbiting Satellite The polar-orbiting satellite circles the Earth over the north and south poles at low altitude (for NOAA, around 850 km) within a short period. As its orbit is lower than those of the geostationary satellites, it can conduct microwave observation. It can observe the polar regions, which the geostationary satellite cannot. It passes over the same point on the earth only twice a day. It observes a swath only about 2,000 km wide centering on the nadir. Satellite pictures are not snap-shots. Scanning takes time. Physical quantities are averaged over pixels. - 70℃ - 80℃ - 40℃ 0℃ 0℃ - 40℃ - 40℃ - 30℃ - 80℃ - 20℃ - 50℃ 2 km (IR) Developing Cb smaller than a pixel cannot be visualized Resolution Latitude 1 km Just under the satellite Longitude Basics of Satellite Imagery Analysis Basics of satellite imagery Review of radiation physics Features of each channel VS IR, I2 WV I4 S1 (IR-I2), S2 (I4-IR) Every physical body emits electromagnetic radiation. There is a relationship between emitted radiation and temperature. Wikipedia Temperature Low High Radiation Energy Relationship between radiation and temperature • Planck’s law • Stefan-Boltzmann's n o i Law t a i I = σ T4 [Wm-2] d a r • Wien's DisplacementLaw λMAX = 2,987 / T [μm] wavelength wikipedia Wien's Displacement Law λ MAX = 2,987 / T [μm] T ~ 6000 K T ~ 300 K λ = 2,987 / 6000 MAX λ MAX = 2,987 / 300 ~ 0.5 [μm] (Visible) ~ 10 [μm] (Infrared) Source: http://www.nasa.gov/images/content/706436main_20121114- 304-193Blend_M6-orig_full.jpg Electromagnetic Spectrum VIS IR 10-9μm 10-6μm 10-3μm 1μm 103μm 1m http://www.colonlove.com/Relax-Far-Infrared-Sauna_ep_41.html Visible channels IR channels ↓ Atmosphere aerosol Radiation from Clouds Absorption by H2O, Radiation from CO2, O3, aerosol Reflection H2O, CO2, O3 Absorption by H2O, CO2, O3 Absorption Reflection from Land/Sea Land/ Sea Atmospheric Absorption (Solar Radiation) VS ↓ Atmosphere aerosol Absorbed by H2O, CO2, O3, aerosol Reflection Absorption Reflection from Land/Sea Land/ Sea Atmospheric Absorption (Earth Radiation) I2 IR WV Absorption by H2O, CO2,O3 An Introduction to Atmospheric Radiation (K. N. Liou, 2002) Land/ Sea Absorption by Atmospheric Gases Meteorology (M. Morgan, 1997) Basics of Satellite Imagery Analysis Basics of satellite imagery Review of radiation physics Features of each channel VS IR, I2 WV I4 S1 (IR-I2), S2 (I4-IR) 16 Bands of AHI (Advanced Himawari Imager) Characteristics of Wavebands VS (0.64 μm) The waveband of the strongest solar radiation IR (10.4 μm) / I2 (12.3 μm) The waveband of the strongest earth radiation with little intermediate absorption and re-emission (atmospheric window) WV (6.2 μm) IR channel with significant absorption by water vapor (Water Vapor channel) I4 (3.9 μm) Affected by both solar radiation and earth radiation. The radiation characteristic for water cloud is different from that of IR1, which enables visualization of low-level cloud (fog) at night. Visible Channel VS (0.64 μm) • Shows intensity of reflected solar radiation (=sunshine). • Appearance depends on solar elevation angle. In the morning and evening and in high-latitude areas, images appear darker because there is little incident light due to oblique sunlight and a low number of reflected rays. VS 00 UTC, 8 October 2014 VS 06 UTC, 8 October 2014 Visible Channel VS (0.64 μm) Usage: • Distinction between thick and thin clouds The reflectance of a cloud depends on the number and density of droplets and raindrops in it. • Distinction between convective and stratiform types Allows identification of cloud types from cloud top surface texture. Smooth and uniform Rugged and uneven Thin Cloud Thick Cloud Thin or Thick? IR VS Thin or Thick? Thin is the correct answer. Thin! IR VS Thin or Thick? IR VS Thin or Thick? Thick is the correct answer. Thick! IR VS Infrared Channels (IR, I2, WV, I4) • Show distribution of brightness temperature. • Each channel has different radiation characteristics. • Colder = lighter (white); warmer = darker (black) • A cloud appears white not because it is a cloud but because it is cold. IR 00 UTC, 8 October 2014 IR 00 UTC, 8 October 2014 I2 00 UTC, 8 October 2014 WV 00 UTC, 8 October 2014 I4 00 UTC, 8 October 2014 Infrared Channels (IR) 300 +20℃ 250 +10℃ 0℃ 200 -10℃ -20℃ 150 -30℃ Example: 100 -40℃ Sensor (IR channel) receives -50℃ 50 10.3-11.3 μm energy at around 10.4 μm. 2. ｴ10- 6 5. ｴ 10-6 0.00001 0.00002 0.00005 I = σT4 300 +20℃ dark 250 +10℃ 0℃ 200 Converted into TBB -10℃ (equivalent Black Body Temperature) 150 -20℃ white -30℃ 100 -40℃ -50℃ 50 2. ｴ10- 6 5. ｴ 10-6 0.00001 0.00002 0.00005 Infrared Channels (IR, I2, WV, I4) Observation of cloud top temperature produces data that can be used to determine cloud top height if the temperature profile is known. 300 250 200 150 100 500 hPa 50 0℃ 2. ｴ 10-6 5. ｴ 10-6 0.00001 0.00002 0.00005 300 10℃ 250 20℃ 0℃ 850 hPa 200 10℃ 150 100 50 31 20℃ 1000 hPa 2. ｴ 10-6 5. ｴ 10-6 0.00001 0.00002 0.00005 31 IR, I2 (Thin Cloud) Total sensor input 300 250 200 Transmission 150 ℃ 0 500 hPa 100 50 600 hPa 5℃ 2. ｴ 10-6 5. ｴ 10-6 0.00001 0.00002 0.00005 300 250 200 150 100 50 2. ｴ 10-6 5. ｴ 10-6 0.00001 0.00002 0.00005 20℃ 1000 hPa Which cloud is higher: A or B? Whiter: colder; darker: warmer IR A B Which cloud is higher: A or B? Whiter: colder; darker: warmer IR Low temperature: higher A B Infrared Difference Imagery (IR - I2) S1 • S1: Yellow Sand, Volcanic Eruption, Thin Ci, etc. S1 00UTC, 8 October 2014 Infrared Difference Imagery (IR - I2) S1 10.4 μm (IR) 12.3 μm (I2) Thin Ci Cloud free area SiO2 Dry Wet Thick Radiation cloud characteristics of quartz (SiO2) Volcanic ash and Blackbody Yellow sand IR1: cleaner window Different transmissivity characteristics IR - I2 (10.4 – 12.3 μm) is 0 Positive =0 Negative Positive ( Gray Black Light gray White Black ) ≃ Features of Cirrus in Satellite Imagery Here, 11 mm is around 3 - 5 [K] higher in Brightness temperature terms of brightness temperature. IR > I2 I2 IR (10.4 mm) - I2 (12.3 mm) 37 Cirrus or Cb? Darker areas are cirrus. Yellow sand Yellow sand forecast Volcanic Ash WV (Water Vapor Channel) Total sensor input The Higher The Colder Re-emission Absorption Upper-level Air Re-emission Absorption Mid-level Air Re-emission Absorption Lower-level Air • Corresponds to the amount of water vapor in the upper and middle layers. • Cannot detect low-level water vapor. Which area is moister: A or B? A WV B B is moister. A WV Minamitorishima/Japan BIAK/Frans B Kaseipo I4 (3.9 μm) Edge of Solar and Earth Radiation 2000 3.9 μm 1750 1500 Very small amount of energy Night: earth radiation only 1250 Day: contaminated by sunlight 1000 750 0.5μm 5800K 10μm 500 290K 250 Solar radiation Earth radiation 5. ｴ 10-7 1. ｴ 10-6 5. ｴ 10-6 0.00001 0.00005 Fire Detection with I4 (3.9μm) T fire = 500K When 5% of a 300 K pixel is 500 K, • 320 K is detected in IR1 (11 μm) T(3.9μm) • 360 K is detected in IR4 (3.9 μm) e r u t a r 320K IR1 IR4 e 360K p T(11μm) more m Less e T affected affected Response functions 300K to fire differ between 11μm 3.9μm IR1 and IR4 1 pixel T surface = 300K 0.05 Sub-pixel Effect Fire Fraction More energy needed n o i t a i d a R Less energy needed Wave length I4 IR What is this? I4 (3.9 μm) IR (10.4 μm) What is the black dot? From Google Maps Volcanic Eruption I4 (3.9 μm) IR (10.4 μm) Eruption of Mt. Raung What are these? I4 (3.9 μm) VS (0.64 μm) What is this gray What are these black area? dots? Here Quoted from Google map What are these? I4 (3.9 μm) IR (10.4 μm) What are these black Nothing dots? Forest Fire I4 (3.9 μm) VS (0.64 μm) Smoke Forest fire 3.9 μm Difference Imagery (I4 - IR) S2 • S2: Fog, Forest Fire, Volcanic Eruption, Convective cloud, etc. S2 00UTC, 8 October 2014 Difference between I4 and IR (Nighttime) I4 IR I4 IR I4 IR I4 IR 3.9 μm10.4 μm 3.9 μm10.4 μm 3.9 μm10.4 μm 3.9 μm10.4 μm Thin Ci Ice Cloud Water Cloud Surface Split image S2 (I4 - IR (3.9 μm – 10.4 μm)) 0 >0 =0 <0 Gray White Gray Black ≃ Fog (night time) IR I4 S2 (I4 - IR) white Gray Black VS Large (Reflection) Small IR, I2 Low (Temperature) High WV Humid (WV amount) Dry I4 Small (Reflection) Large (daytime) I4 Low (Temperature) High (night time) S1: IR – I2 < 0 (negative) = 0 > 0 (positive) S2: I4 – IR < 0 = 0 > 0 E N D.