Remote Sensing Fall 2010 Meteorology 311What is it? • Measurement using devices not in direct contact with the object they sense. – Remote sensing involves observing objects indirectly either actively or passively. • In-Situ measurements: Devices in contact with the medium they are sensing. • Anemometer, Satellite, camera, radar, thermometer, windsock, hand in boiling water, lidar, metal detector, x-ray • In-Situ meaurements: measure atmospheric conditions at discrete locations/points and time. – Gaps in the observation network.Types of SensingSatellite Observations • Geostationary : Remains stationary over a specific point on the earth – GOES (Geostationary Operational Environmental Satellite) – Cover a region of interest defined by the owner. – Elevation ~ 22,000 miles above sea level. – Less detail than POES, but provides many more images. • Polar-Orbiting or Low-Earth Orbiting : Track from pole to pole. – Do not cover the same area. – Cover small strips. Each pass sees an area to the west of previous pass. – Sun synchronous: path does not change with respect to sun relative coordinate system. – Elevation ~ 600 miles (complete rotation about every 1.5 hours). – Passes any point on earth twice a day. – NOAA uses two of these so no image is over six hours old. – Great detail, but only sample a given area a few times per day.Visible Images • Record visible light from the sun that is reflected from cloud, land, oceans, snow, or ice. – Albedo. – λ = 0.52 – 0.72 microns. • Bright clouds indicate a lot of reflecting particles. • High and low clouds look equally as bright and are often indistinguishable.Visible Images - Albedos • Thunderstorm – 80-90% • Cumulus – 70% • Stratus – 60% • Thin stratus – 50% • Cirrus – 40% • Thin cirrus – 30% • Smoke – 20% • Blackbody – 0 % • Fresh snow cover – 80% • White Sands, NM – 60% • Melting snow, salt flats -50% • Dry, sandy soil – 40% • Clay, granite, glaciers – 30% • Tundra, bare soil – 20% • Oceans, lakes, forest – 10%Visible ImageVisible ImageryVisible ImageryInfrared Images • Record blackbody temperature of an object. – Amount of radiation ~ T4. – Measures λ = 10.2-11.2 microns = 10.2-11.2 μm. • Show cloud top temperature in cloudy regions, and, possibly, surface temperature in clear regions. • Bright clouds are COLD clouds, which are usually high. • Low clouds are hard to distinguish from the surface. Why?Infrared ImagesComparisonIR ImageryWater Vapor Images • Integrated measure of moisture in the atmosphere. – Measures amount of raditation emitted at 6.7 microns = 6.7 μm. – Water vapor heavily absorbs radiation at this wavelength. • Absorption is greatest in the mid/upper troposphere between 600 and 250 mb. • Good measure of mid/upper level moisture. • Impossible to draw conclusions about low level moisture. • Look for regions of changing characteristics (drying/moistening).Water Vapor ImageComparison