GEOG/GEOL 4093 Remote Sensing of the Environment Midterm Review Outline • List of key concepts • Introductory Information • Electromagnetic radiation and its interaction with matter • Platforms for Remote Sensing • Aerial & Space Photography • Imaging Systems, Passive Sensors • Imaging Systems, Active SensorsList of key concepts  Definition of remote sensing, and why we us it  Different types of remote sensing platforms and their advantages/disadvantages  Active vs. passive remote sensing. Imaging vs. non-imaging  Polarization  Frequency, wavelength  Different regions of the Electromagnetic Spectrum (UV, visible, Infrared, microwave, radar)  Emissivity, blackbody, and gray body  Relationship between emitted energy, temperature, and wavelength (Planck’s function, and Stefan-Boltzman’s law)  Relationship between peak wavelength and temperature (Wein’s Displacement Law)  Interactions of EMR with matter  Albedo, reflection, emission, transmission, scattering, specular, diffuse  Extinction and attenuation  Atmospheric window and absorption bands  Spectral signatures  Types of scattering (Mie, Rayleigh, Non-selective), their similarities and differences, the associated relationships between particles and wavelengths  Types of orbits (geostationary, geosynchronous, sun-synchronous, molniya), their relative velocities, and their approximate altitudes  Focal plane, focal lengthList of key concepts  How we use films, detectors and filters to customize our observations  Panchromatic, infra-red, and color film  Panchromatic vs. multi-spectral remote sensing  Additive colors (primary, complementary, and how they mix)  Four Different types of resolution and the things that control them  Different characteristics of remote sensing in the different parts of the spectrum, such as spatial resolution, ability to penetrate the atmosphere, ability to penetrate a surface  Types of scanning (whiskbroom, pushbroom, conical), and different characteristics of each  Characteristics of passive microwave  Basic concept of Synthetic Aperture Radar (SAR) and how it achieves high resolution  What controls the amount of backscattered radar energy  Slant-range distortion, layover, foreshortening, shadowing  Sensors and satellites that work in different parts of the spectrum (e.g. Landsat (TM, ETM+, MSS), AVHRR, SSM/I, GOES, ATSR, Radarsat).  Spatial, temporal, spectral and radiometric resolution of different sensors (including commercial satellites)  Basic idea of scatterometry  Why we use multiple channels or multiple viewing angles to determine surface temperature  Various applications of different sensor channels (i.e. what part of the spectrum we use for what applications, and what instruments operate in these regions)?Short definition of Remote Sensing • Remote sensing is the collection of information about an object or system without coming into direct physical contact with it • That information is nearly always carried by electromagnetic radiation (EMR)Why do we do remote sensing? •Unobtrusive •Automated •Useful for extreme conditions •Offers excellent spatial and temporal coverage •Extends our senses •Near Real-time •No “Political” Boundary •Often cost effectiveRemote Sensing Systems • Active Sensor – illuminates subject from an artificial (on-board) energy source • Passive sensor – uses naturally emitted radiation from the sun or the object being observed • Imaging sensor – creates a “picture” by scanning across a linear array of detectors while the array moves through space • Non-imaging sensors = measures along a transect or at a point.Electromagnetic radiation and its Interaction with matterThe Electromagnetic Spectrum • EMR used in remote sensing Diagram shows those of the EM spectrum which is important in remote sensing The lower graphs shows the atmospheric transmission of the EMR versus wavelength (log-scale)n = frequency Electric field Transmission direction Amplitude c = nl l = distance of separation between two wave peaks n = number of wave peaks passing in a given time c = speed of light Frequencies and wavelengths Electromagnetic Wave PropertiesProperties of Electromagnetic Radiation • The orientation of the electric field is termed polarization and is important in discussing the operation of remote sensing system Vertical Polarization (V): electric vector is perpendicular to the plane of incidence Horizontal polarization (H): electric vector is parallel to the plane of incidence • Radiation from the Sun is unpolarized (at random) • Man made sources (laser, radar) have polarized radiationBasic Laws Planck’s law (Spectral Radiance) Stefan-Bolzmann law (TIR) • The total emitted energy over the whole spectrum is proportional the physical temperature M = esT4 M = sT4 Blackbody GraybodyBasic Laws Blackbody - Object that absorbs and emits 100 % of radiation - Does not exist in nature - Emissivity would equal one Graybody - Object that reflects part of the incident radiation - Emissivity is smaller than one Emissivity • Describes the actual absorption and emission properties of real objects (“gray bodies”) • Is wavelength dependent • Is equal to (graybody emittance)/(blackbody emittance) • Establishes an object’s radiant temperature (Trad ) or brightness temperature Trad = ε1/4Tkin ε = ( Trad / Tkin)4• Sun’s temperature = 6000 K the wavelength of peak emittance = 2898 mm K/6000 K = 0.48 mm • Earth’s temperature = 300 K the wavelength of peak emittance = 2898 mm K/300 K = 9.6 mm Wien’s displacement law : lmax = k/T Basic Laws k = 2898 mm K Source:Chuvieco and Huete 2010EMR Interaction With Matter Radiative properties of a natural surface • Radiation incident upon a surface must either be transmitted (t) through it, reflected (a) from the surface or be absorbed (z). • For solar radiation, a is referred to as the surface albedo • If we consider only part of the EM spectrum, a is referred to as the spectral albedo • Albedo is the percent of incident solar energy that is reflected from a surface Transmissivity + Reflectivity + Absorptivity = 1Attenuation The reduction of Intensity of EMR as it passes through a medium. Sometimes called extinction (Combination