Lecture 4: Meteorological Satellites and Instruments. Acknowledgement: Dr. S. Kidder at Colorado State Univ.

Transcription

1 Lecture 4: Meteorological Satellites and Instruments Acknowledgement: Dr. S. Kidder at Colorado State Univ.

2 Homework for the Spring Break: get some tangible, preliminary results for your final project.

3 Outline 1. Meteorological Satellites: Operational Vs Experimental 2. Operational Satellites: Polar Orbiting Satellites and Geostationary 3. Experimental Satellites: Some Examples We focus on 1) what measurements these satellites/ instruments make and 2) what physical principles are behind these measurements. Less emphasis is placed on the engineering aspects of the instrumentation design.

4 Types of Artificial Satellites 1. Astronomical satellites 2. Biosatellites 3. Communication satellites 4. Navigational satellites 5. Earth Observation Satellites 6. Reconnaissance Satellites (military) 7.

5 Astronomical Satellite: Hubble Space Telescope wikipedia.org Navigational satellite: GPS

6 Meteorological Satellites 1. Astronomical satellites 2. Biosatellites 3. Communication satellites 4. Navigational satellites 5. Earth Observation Satellites 6. Reconnaissance Satellites (military) 7. Meteorological Satellite: targets are meteorological variables - temperature, humidity, winds, precipitation, clouds, etc. So, we need spectra that are sensitive to these targets. These are also other Earth Observation Satellites which focus on land surface, ocean, etc.

7 Operational Vs Experimental Operational: designed for day-to-day operations of weather services. High requirements on reliability and availability. In USA, the agency that administrates operational MetSat is NOAA (National Oceanic & Atmospheric Administration). DoD also has its own operational MetSat. Experimental: designed to test new concept or technology. May find its use in meteorological service in the future. NASA is the main space agency of this country that develops experimental satellites.

8 Think-Pair-Share: which direction does this satellite travel (left to right or right to left)?

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10 Operational Vs Experimental Operational: designed for day-to-day operations of weather services. High requirements on reliability and availability. In USA, the agency that administrates operational MetSat is NOAA (National Oceanic & Atmospheric Administration). DoD also has its own operational MetSat. Experimental: designed to test new concept or technology. May find its use in meteorological service in the future. NASA is the main space agency of this country that develops experimental satellites.

11 Five Geostationary (GEO) satellites are sufficient for covering the whole Earth (except the polar region) and monitoring fast-evolving features Courtesy: NCAR

12 Courtesy: NCAR

13 US US EU EU Japan Courtesy: Navy Research Lab

14 LEO satellites covering polar regions (aka polar orbiters) and measuring relatively slowing-evolving variables (because they hit and miss) Polar orbiters

15 LEO satellites view of the Earth is very different from that of the GEO satellites: its snapshot covers a much smaller area, but at a closer range, instrumentation designs become easier. Besides, LEO views the poles. ~ 36,000 km LEO GEO ~ 800 km Courtesy: ESA

16 LEO s view Courtesy: ESA GEO s view

17 NOAA maintains two polar orbiters, one crosses the equator at 7:30 AM/PM and the other 1:40 AM/PM, so every spot on Earth (except polar region) is sampled 4 times per day. NP/SP are viewed for each orbit (~ 2 hrs). But situation will change soon Courtesy: ESA

18 NOAA Polar Orbiters: All started with TIROS (Television Infrared Observation Satellite) in 1960, followed by TIROS N and Advanced TIROS N. From 1970, these polar orbiters are known as NOAA-1,2,3, and so on. Now, we have NOAA-19 in service. NOAA polar orbiters have gone through evolution and improvements, but instrument functions stay similar. We will use TIROS N as an example for illustration. The following instruments are carried: 1. AVHRR (Advanced Very High Resolution Radiometer) 2. HIRS (High Resolution Infrared Radiation Sounder) 3. MSU (Microwave Sounding Unit) 4. SSU (Stratosphere Sounding Unit) 5. SBUV (Solar Backscatter Ultraviolet Radiometer)

19 AVHRR: imager, taking pictures of the Earth. HIRS/MSU: sounder, performing atmospheric sounding, that is, collecting vertical distribution of physical properties of the atmosphere (e.g., temperature, moisture, etc.) Imagers have finer resolution than sounders because the they are designed to capture horizontal fine structure of the atmosphere and the surface, whereas sounders are for remote sensing of atmospheric vertical structures. Temperature profile of the atmosphere doesn t change much over a horizontal range of, say, 30 km. Large changes in temperature across this image need high horizontal resolution.

20 Imager Sounder Visible picture of the surface or clouds. IR picture of the surface or clouds Several IR channels in combination to give pictures of different levels of the atmosphere Total absorption Total Transmission IR window µm

21 AVHRR Channels: all windows Total absorption Zero absorption

22 AVHRR: a cross scanning radiometer

23 Resolution/coverage of AVHRR 1. Ground resolution: ~ 1 km at nadir 2. Scanning swath width: ~ ±1500 km Hurricane Florence from AVHRR Courtesy: Steven Babin

24 HIRS (High Resolution Infrared Radiation Sounder)

25 Height (km) Weighting Function (1/km) I = I 0 Tr * 1µ + h 0 B( T)W ( h,µ )dh

26 CO 2 Slicing: 7 channels along the slope of transmissivity, each sensitive to a certain layer of the atmosphere

27 Resolutions: AVHRR Vs HIRS/2 AVHRR (imager): 1.1 km at nadir, km at the end of the scan HIRS (sounder): 18.5 km at nadir, km at the end of the scan Scanning pattern of HIRS

28 MSU (microwave sounding unit) Microwave channels have the advantage of being able to penetrate clouds, whereas IR can t.

29 Challenge facing microwave instruments Limiting Resolution (Rayleigh Criterion) ΔΘ = 1.22 λ / D ΔΘ = smallest angular separation that can be resolved λ = wavelength being observed D = diameter of the lens Human eye: D = 3 mm, λ = 0.45 µm (visible spectrum): ΔΘ = 0.2 mrad. At 1 meter distance corresponds to a resolution of ~0.2 mm. This equation is particularly limiting for satellite microwave instruments since λ 1 cm = 10,000 µm

30 MSU AVHRR (imager): 1.1 km at nadir HIRS (sounder): 18.5 km at nadir MSU: km at nadir (newer version called AMSU has higher resolution)