1 Remote Sensing Principles and ApplicationsApril 15, Youngwook Kim

2 What is Remote Sensing? The measurement or acquisition of information of some property of an object or phenomenon, by a recording device that is not physical or intimate contact with the object or phenomenon under study (ASPRS 1983) Acquisition of information about the condition and/or the state of a target by a sensor that is not in direct physical contact with it (Asrar 1989) Remote sensing (RS) is the acquisition of information about an object or phenomenon without making physical contact with the object. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth (both on the surface, and in the atmosphere and oceans) by means of propagated signals (e.g. electromagnetic radiation emitted from aircraft or satellites) (Wikipedia)

3 Where is Remote Sensing?Three-way interaction model between spatial science as used in the physical, biological, and social sciences Jensen, 2000

4 Remote Sensing ProcessJensen, 2004

5 What is remote sensing useful?A synoptic view of a large area Access to regions that are not accessible to in situ. Approaches Global coverage Periodical monitoring Collecting data at wavelengths that our eyes do not respond

6 Electromagnetic SpectrumUltraviolet (UV) – less than 0.35 µm Visible – 0.35 to 0.70 µm (350 to 700 nm) Near Infrared (NIR) – 0.7 to 1.1 µm Shortwave Infrared (SWIR) – 1.1 to 2.5 µm Thermal Infrared (TIR) – 8.0 to 16.0 µm ●Also called LWIR ●Emissive portion of the spectrum Visible and near infrared (VNIR) – 0.35 to 1.1 µm (region over which silicon detector work well) Solar reflective – VNIR and SWIR – 0.35 to 2.5 µm (region where reflected solar energy dominates the problem) Microwave region – 1 mm to 1 m (300 GHz to 300 MHz)

7 The Concept of Remote SensingSun Sensor EMR Objects Energy recorded by remote sensing systems undergoes fundamental interactions that should be understood to properly interpret the remotely sensed data The remotely sensed energy (EMR) comes from the Sun ●is radiated by atomic particles from the Sun (source), ●propagates through the vacuum of space at the speed of light, ●interacts with the Earth’s atmosphere ●interacts with the Earth’s surface ●interacts with the Earth’s atmosphere once again, and ●finally reaches the remote sensor We can illustrate the main elements of a remote sensing system with a simple example involving the following components; an energy source (the Sun), an observed object (a tree), a sensor (our eye), and the flow of electromagnetic energy from the Sun to the object and to the sensor. In this example, we are able to observe the tree by means of reflected sunlight and we could have also employed artificial sources of light to illuminate the tree (e.g., a flashlight). Our eyes can also sense the energy that originates from and is emitted from the object itself, as in the case of fires. In remote sensing we often consider three ways of ‘sensing’ information about an object: (a) by reflection, (b) by emission, and (c) by combined emission-reflection (Fig. 2.1.). The first of the three is the most important in remote sensing since it utilizes sunlight, the main source of energy on our planet. The Sun illuminates the Earth’s surface, which in turn reflects a portion of this energy back to space in a manner dependent on the composition and structure of the land cover present on the surface. The reflected electromagnetic energy is detected by the orbiting, space-based sensor, which then records and transmits this signal to a receiving station or satellite dish. In general, the flow of energy from one place to another may also occur through convection, conduction, and latent energy in addition to electromagnetic radiation. In remote sensing, we mostly focus on the measurement and information content of the electromagnetic radiation signal. The remotely-sensed information, however, may be coupled with the other energy terms to yield measures of evapotranspiration, photosynthesis, and soil moisture.

8 Effect of the Atmosphere on RadiationAtmosphere can refract, scatter, and absorb Refraction refers to the bending of radiation from its original path ●Only a major factor in long path lengths through the atmosphere Scattering refers to the redirection of radiation after interaction with a particle in the atmosphere ●a function of the wavelength of the incident radiation and the size of a particle (e.g., gas molecule, dust, water vapor) encountered Absorption is the incorporation of the radiation within the particle to alter the energy state of the particle ●Gaseous absorption and aerosol absorption ●Gases that cause the largest impact to RS are CO2, H2O, and O3 ▪Wavelengths (<0.3 µm) are almost completely absorbed (e.g., O3) ▪CO2: greenhouse gas (infrared radiation absorption) ▪H2O: NIR, SWIR, far-infrared and microwave regions Scattering and Absorption are referred to as attenuation or extinction Infrared Atmospheric window (8-12 µm) can penetrate the earth’s atmosphere Rayleigh scattering occurs when the diameter of the matter (usually air molecules) are many times smaller than the incident electromagnetic radiation. This type of scattering is named after the English physicist who offered the first coherent explanation for it. All scattering is accomplished through absorption and re-emission of radiation by atoms or molecules in the manner described in the discussion on radiation from atomic structures. It is impossible to predict the direction in which a specific atom or molecule will emit a photon, hence scattering. Rayleigh scattering is responsible for red sunsets. Since the atmosphere is a thin shell of gravitationally bound gas surrounding the solid Earth, sunlight must pass through a longer slant path of air at sunset (or sunrise) than at noon. Since the violet and blue wavelengths are scattered even more during their now-longer path through the air than when the Sun is overhead, what we see when we look toward the Sun is the residue - the wavelengths of sunlight that are hardly scattered away at all, especially the oranges and reds (Sagan, 1994). Mie scattering takes place when there are essentially spherical particles present in the atmosphere with diameters approximately equal to the wavelength of radiation being considered. For visible light, water vapor, dust, and other particles ranging from a few tenths of a micrometer to several micrometers in diameter are the main scattering agents. The amount of scatter is greater than Rayleigh scatter and the wavelengths scattered are longer. Pollution also contributes to beautiful sunsets and sunrises. The greater the amount of smoke and dust particles in the atmospheric column, the more violet and blue light will be scattered away and only the longer orange and red wavelength light will reach our eyes. Non-selective scattering is produced when there are particles in the atmosphere several times the diameter of the radiation being transmitted. This type of scattering is non-selective, i.e. all wavelengths of light are scattered, not just blue, green, or red. Thus, water droplets, which make up clouds and fog banks, scatter all wavelengths of visible light equally well, causing the cloud to appear white (a mixture of all colors of light in approximately equal quantities produces white). Scattering can severely reduce the information content of remotely sensed data to the point that the imagery looses contrast and it is difficult to differentiate one object from another.

9 Atmospheric TransmittanceTransmittance: the fraction of incident EMR at a specified wavelength that passes through a sample (e.g., Earth atmosphere) How well the atmosphere lets radiation pass will determine what measurements of the surface can be made Spectral regions with poor transmittance are good for atmospheric sensing, not good for terrestrial remote sensing

10 Resolution Four basic types- Spatial, Temporal, Radiometric, SpectralTemporal resolution ●Frequency of the data collection (repeat cycle and revisit time) ●How long the sensor is on over target (integration time or shutter speed) ●Mission lifetime or operation period Radiometric resolution ●Sampling changes in energy levels ●Smallest detectable change in energy ●Minimum and maximum detectable energy levels (Dynamic Range) Spectral resolution ●Band spacing ●Narrowest band width ●Overall spectral coverage Spatial resolution ●Spatial sampling of data points (Ground sampling interval – GSI) ●Smallest area sampled (Pixel size, Ground Instantaneous Filed of View-GIFOV, Ground Sampling Distance-GSD) ●Full area covered by the sensor (swath width)

11 Temporal Resolution June 1, 2001 June 17, 2002 July 3, 2003 16 daysRemote Sensor Data Acquisition June 1, 2001 June 17, 2002 July 3, 2003 16 days Jensen, 2000

12 Radiometric Resolution8-bit ( ) 9-bit ( ) 10-bit ( ) Jensen, 2000

13 Spectral Resolution Jensen, 2000

14 Spatial Resolution Swath width refers to the strip of the Earth’s surface from which geographic data are collected by a moving vehicle such as a satellite, aircraft or ship in the course of swath mapping (Wikepedia) Jensen, 2000

15 Satellite Orbits Typical orbits are Polar Geo-synchronousSun-synchronous Sun-synchronous orbit

16 Calibrations and correctionsTypes of calibration- Geometric and Radiometric Geometric calibration: pixels location in latitude and longitude and height Radiometric calibration allows the sensor output to be converted to an absolute scale VNIR/SWIR atmospheric correction Sun angle is a critical factor in the VNIR/SWIR Proper atmospheric correction in the VNIR/SWIR allows direct comparison to two scenes to determine changes in surface characteristics ●Removes effects due to view and solar angles ●Changes in atmospheric conditions are taken into account (aerosol amounts, water vapor content, etc)

17 Current Satellite Systems and Sensors NASA currently has a fleet of 16 remote sensing observatories orbiting Earth. The satellites include components of the A-Train (Terra, Aqua, Aura, CloudSat, CALIPSO), two satellites launched in 2011 (Aquarius, Suomi NPP), and nine others (ACRIMSAT, SORCE, GRACE, Jason-1 and 2, Landsat 7, QuikSCAT, TRMM, and EO-1). These satellites measure tropical rainfall, solar irradiance, clouds, sea surface height, ocean salinity, and other aspects of the global environment. Together, they provide a perspective of the Earth as a system.

18 Current Satellite Systems and SensorsMultispectral Remote Sensing is the collection of reflected, emitted, or backscattered energy from an object or area of interest in multiple bands of the electromagnetic spectrum. AVHRR, MODIS, SPOT, Landsat, ASTER, IKONOS, Quickbird Active and passive microwave sensors

19 Multispectral sensors: Moderate and coarse resolutionMODIS Moderate Resolution Imaging Spectroradiometer Platform: EOS Terra and Aqua Pixel resolution: 250, 500, and 1000 m (~6 km at edge) Overpass times: 10:30 (Terra) and 13:30 (Aqua) Spectral bands: 36 Started: 2000 Terra-MODIS TerraMODIS swath Coverage 2330km Global change research investigates the underlying processes of change and their manifestation, the impacts and the prediction of change. Monitoring of land cover and land use is an important element of the NASA Earth Science Enterprise. Provide important inputs to parameterize or validate ecosystem process models.  High quality, consistent and well-calibrated satellite measurements are needed if we are to detect and monitor changes and trends in these variables. Developing the next-generation data sets for global change research

20 MODIS Global change research investigates the underlying processes of change and their manifestation, the impacts and the prediction of change Monitoring of land cover and land use is an important element of the NASA Earth Science Enterprise Provide important inputs to parameterize or validate ecosystem process models.  High quality, consistent and well-calibrated satellite measurements are needed if we are to detect and monitor changes and trends in these variables Developing the next-generation data sets for global change research

21 MODIS Key Specifications (MODIS Instruments are meeting specs)

22 MODIS Products MOD01 Level-1A Radiance CountsMOD02 Level-1B Calibrated Relocated Radiances -also Level 1B “subsampled” 5kmX5km pro MOD03 Geolocation Data Set MOD04 Aerosol Product MOD05 Total Precipitable Water MOD06 Cloud Product MOD07 Atmospheric Profiles MOD08 Gridded Atmospheric Product (Level 3) MOD09 Atmospherically-corrected Surface Reflectance MOD10 Snow Cover MOD11 Land Surface Temperature & Emissivity MOD12 Land Cover/Land Cover Change MOD13 Vegetation Indices MOD14 Thermal Anomalies, Fires & Biomass Burning MOD15 Leaf Area Index & FPAR MOD16 Surface Resistance & Evapotranspiration MOD17 Vegetation Production, Net Primary Productivity MOD18 Normalized Water-leaving Radiance MOD19 Pigment Concentration MOD20 Chlorophyll Fluorescence MOD21 Chlorophyll_a Pigment Concentration MOD22 Photosynthetically Active Radiation (PAR) MOD23 Suspended-Solids Conc, Ocean Water MOD24 Organic Matter Concentration MOD25 Coccolith Concentration MOD26 Ocean Water Attenuation Coefficient MOD27 Ocean Primary Productivity MOD28 Sea Surface Temperature MOD29 Sea Ice Cover MOD Temperature and Moisture Profiles MOD32 Processing Framework & Match- up Database MOD Gridded Snow Cover MOD Gridded Vegetation Indices MOD35 Cloud Mask MOD36 Total Absorption Coefficient MOD37 Ocean Aerosol Properties MOD39 Clear Water Epsilon MOD43 Albedo 16-day L3 MOD44 Vegetation Cover Conversion

23 MODIS Global GPP/NPP http://ntsg.umt.edu/project/mod17GPP: Gross primary production (gC/m2/d) PAR: Photosynthetically active radiation FPAR: Fraction of PAR MODIS GPP/NPP is the first continuous satellite-derived dataset monitoring global vegetation productivity. Continuous and accurate measurements of terrestrial NPP at the global scale are possible using satellite data. Since early 2000, for the first time, the MODIS sensors onboard the Terra and Aqua satellites, have operationally provided scientists with near real-time global terrestrial gross primary production (GPP) and net photosynthesis (PsnNet) data. These data are provided at 1 km spatial resolution and an 8-day interval, and annual NPP covers 109,782,756 km2 of vegetated land. These GPP, PsnNet and NPP products are collectively known as MOD17 and are part of a larger suite of MODIS land products (Justice et al. 2002), one of the core Earth System or Climate Data Records (ESDR or CDR). These products have improved based on extensive validation and calibration activities by the MODIS science team. The Collection-5 (C5) MODIS data are being reprocessed by NASA in 2007 and will have higher quality than the previous collections. : Net photosynthesis, an intermediate variable between GPP and NPP : Maintenance respiration from living leaves and fine roots (gC/m2/d) : Light use efficiency parameter (gC/MJ) : Downward surface solar shortwave radiation (MJ/m2/d) : Maximum e under optimal conditions (gC/MJ) : Annual maintenance respiration from living wood (gC/m2/d) : Daily minimum temperature scalar : Vapor pressure deficits (VPD) scalar NPP: Annual net primary production (gC/m2/yr)

24 MODIS Global Evapotranspiration The MOD16 ET algorithm is based on the Penman-Monteith equation (Monteith, 1965) Terrestrial ET includes evaporation from wet and moist soil, from rain water intercepted by the canopy + the transpiration through stomata on plant leaves and stems

25 Remote Sensing ApplicationsVegetation Indices Radiometric measures of the amount, structure, and condition of vegetation, Precise monitoring tool phenology inter-annual variations Serve as intermediaries in the assessment of various biophysical parameters green cover, biomass, leaf area index (LAI), fAPAR chlorophyll conc.

26 Theoretical Basis With increasing presence of active, p.s. vegetationreflectance in the red (chlorophyll absorption) with simultaneously increasing reflectance in the NIR (leaf structure). We can ratio the 2 spectral regions, linearly combine them, use derivatives, or some combination of above.

27 NDVI Applications The NDVI has been widely used in various operational applications, including famine early warning systems, land cover classification, health and epidemiology, drought detection, land degradation, deforestation, change detection and monitoring.

28 Near Real-time Data

29 MODIS Land Subsets

30 AVHRR The Advanced Very High Resolution Radiometer (AVHRR) is a broad-band, four or five channel (depending on the model) scanner, sensing in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum. This sensor is carried on NOAA's Polar Orbiting Environmental Satellites (POES), beginning with TIROS-N in 1978. Wikipedia

31 AVHRR Spectral Characteristics

32 AVHRR Data

33 SPOT-VGT Data Satellite Pour l’Observation de la Terre Vegetation

34 Multispectral sensors: Fine resolution sensors

35 DAAC (Distributed Active Archive Center) https://lpdaac.usgs.gov/ EODIS Data Centers Map In August, 2005 Hurricane Katrina devastated the Southern U.S. coast and the resulting damage was the costliest storm damage in U.S. history. Portions of Landsat satellite data, acquired and processed by the U.S. Geological Survey illustrate the extent of the flooding in the New Orleans area and the long term impact of the storm. In the September, 2005 image dark tones represent flooded areas of the city. By October, 2005 significant areas are drying; however, the light brown tones represent areas where vegetation (trees, lawns, parks) has been destroyed. By September, 2009 the brown tones are replaced with more green colors, representing new growth of vegetation as neighborhoods rebuild. Federal, state and local officials use the Landsat data to monitor the effects of change and will use the imagery for planning of rehabilitating the region.

36 NASA’s Earth Observing System Data and Information System

37 Active and passive sensorsPassive sensors rely on the ultimate source of energy being supplied by something external to the sensor while active systems use their own source of energy to supply the energy that is measured Passive case Radar, including synthetic aperture radar (SAR), and lidar: the most common active approaches in remote sensing Active systems can readily use wavelengths unaffected by clouds Types ●Imaging radar: similar to a photograph taken by a camera, but taken radar waves (e.g., RADARSAT-1, SAR instrument) ●Non-imaging radar: measures the amount of backscatter, scatterometer (e.g., QuikSCAT) ●Altimetry: measures the time it takes to return to the sensor from sending a pulse of radar energy toward the earth (e.g., ICESat)

38 Landscape Freeze/Thaw Dynamics

39 Phenology https://usanpn.org/

40 Global Land Cover Facility MODIS Vegetation Continuous Fields -indicating the combination of tree and herbaceous vegetation cover and bare ground

41 Useful web references •Federation of American Scientists •CRISP •"Fundamentals of Remote Sensing Tutorial Notes:" •NOAA Center for Satellite Applications and Research •NASA Earth Observatory NASA