Presentation on theme: "Remote sensing technique"— Presentation transcript:
1Remote sensing technique in coastal studiesElena MauriOGS, Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Trieste, ItalyLecture 19
2OUTLINE Electromagnetic spectrum and black body emission Satellite orbits and samplingPASSIVE REMOTE SENSING:in the visible bands (Ocean Color), principles, atmospheric contamination, algorithms to retrieve chlorophyll concentrationpan-spectral, multi-spectral and hyper-spectral sensors and applications (MODIS, Landsat7)in the thermal infrared bands (Sea Surface Temperature) principles, atmospheric effects, algorithms to retrieve SSTapplications (AVHRR and MODIS)ACTIVE REMOTE SENSING:in the microwave bands (Satellite Altimetry and Synthetic Aperture Radar) principles applications (geostrophic surface circulation oil spill detection, etc.)
3Remote Sensing is the science and art of obtaining information about an object, area, or phenomenonthrough the analysis of data acquiredby a device that is not in contact with the object, area, or phenomenon under investigation.Satellite Remote Sensing uses electromagnetic radiation to measure near-surface ocean properties
5Plank’s Law & Blackbody Emission Planck's law describes the spectral radiance of electromagnetic radiation at all wavelength from a black body at temperature T.Black body when is cold no light is reflected or transmitted, the object appears black. When is hot, it will on average emit exactly as much as it absorbs, at every wavelength.As the temperature decreases, the peak of the black-body radiation curve moves to lower intensities and longer wavelengths.Passive remote sensing
9Satellite orbitsPolar-orbiting and geostationary Satellites
10Satellite Remote Sensing Passive and ActiveSatellite Remote SensingPassive (VIS, IR, MW)Active (MW)Links:
11Satellite sensors Scanning Pushbroom Satellite Sampling Instantaneous Field of View (IFOV)Satellite SamplingLinks:
12Oceanographic Platform Sensor Calibrations and Ground TruthIn-situ measurements are needed for ground truthing or validation of remotely sensed dataOceanographic Platform(Ocean color)Surface drifter (SST)Links:
13Sunlight propagation, refection and absorption by atmosphere and ocean Passive remote sensing: VISIBLE
14Remote sensing in the VISIBLE OCEAN COLOR Passive remote sensing: VISIBLERemote sensing in the VISIBLE OCEAN COLOROcean color is not the color we normally see, blue/gray due to the reflection of the sky.BUTOcean color is the color that would be observed freed from the surface reflection, for instance the color measured beneath the surface of the water.
15Remote sensing reflectance (Rrs) Passive remote sensing: VISIBLERemote sensing reflectance (Rrs)Eu (λ)Ed (λ)Is the ratio between the irradiance upwelling just under the surface of the water Eu (λ), to the downwelling irradiance just penetreting the surface Ed (λ).Rrs=
16Remote Sensing Reflectance and inherent optical properties Passive remote sensing: VISIBLERemote Sensing Reflectance and inherent optical propertiesbb(λ)bb(λ) + a(λ)Where: a(λ)=aw(λ)+aph(λ)+ad(λ)+acdom(λ)bb(λ)=bbw (λ)+bbp (λ)Rrs(λ)=constAbsorption is the process by which the enery of a photons is taken up by another entity, for example, by an atom whose valence electrons make transition between two electronic energy levels. The photon is destroyed in the process.Scattering is a general physical process whereby radiation are forced to deviate from a straight trajectory.
17Absorption Passive remote sensing: VISIBLE Relative contribution of absorption by phytoplankton, aph(), and by organic detritus, adet() or ad(), to the total particulate absorption, ap(), from Sargasso Sea waters at 20 m depthTotal absorption spectrum of an idealized, productive (<chl> = 1 mg m-3) oceanic water together with spectra of the individual absorbing components.
18Back-scattering blue green red Passive remote sensing: VISIBLE Clean ocean water (A) has maximum backscatter in short (blue) wavelength and almost zero inyellow and red.Higher is phytoplankton (i.e., chlorophyll and other plant pigments) concentration, more is contributionof green color (B).In coastal zones with high concentration of dead organic and inorganic matter light spectrum hasmaximum in red (C).
20MODIS Moderate-resolution Imaging Spectroradiometer Passive remote sensing: VISIBLEMODISModerate-resolution Imaging Spectroradiometeris on board of two satellite: Terra (EOS AM) satellite (1999),AQUA (EOS PM) satellite (2002).there are 36 spectral bands ranging in wavelength from 0.4 μm to 14.4 µm and at varying spatial resolutions (2 bands at 250 m, 5 bands at 500 m and 29 bands at 1 km).together the instruments image the entire Earth every 1 to 2 days.designed to provide measurements in large-scale global dynamics including changes in Earth's cloud cover, radiation budget and processes occurring in the oceans, on land, and in the lower atmosphere.SpecificationsOrbit705 km, 10:30 a.m. descending node (Terra) or 1:30 p.m. ascending node (Aqua), sun-synchronous, near-polar, circularScan Rate20.3 rpm, cross trackSwath2330 km (cross track) by 10 km (along track at nadir)DimensionsTelescope17.78 cm diam. off-axis, afocal (collimated), with intermediate field stopSize1.0 x 1.6 x 1.0 mWeight228.7 kgData Rate10.6 Mbit/s (peak daytime); 6.1 Mbit/s (orbital average)Spatial Resolution250 m (bands 1-2) 500 m (bands 3-7) 1000 m (bands 8-36)Design Life6 years
21MODIS spectral bands and athmospheric effects Passive remote sensing: VISIBLE
35MODIS chlorophyll concentration around Tanzania Passive remote sensing: VISIBLEMODIS chlorophyll concentration around Tanzania
36Ocean Color Spatial and seasonal (monsoon) variability of the Passive remote sensing: VISIBLEOcean ColorSpatial and seasonal (monsoon) variability of thechlorophyll-a concentration in NW Atlantic and Indian Oceans
37Remote sensing in the VISIBLE Passive remote sensing: VISIBLERemote sensing in the VISIBLETruecolor is a method of representing image (especially in computer processing) in an RGB color space. MODIS res. 250 mMultispectral is a type of sensor with sensitive to a few specific wavelength and hyperspectral sensitive to many (can reach 200 bands) specific bandsPanchromatic sensor is a type of sensor that is sensitive to all wavelength of visible light. This imagery is of a much higher resolution than the multispetral imagery. For example, the QuickBird satellite produces panchromatic imagery having a pixel equivalent to an area 0.6m x 0.6m, while the multispectral pixels represent an area of 2.4m x 2.4m. QuickBird and IKONOSPansharpening is a process of merging high resolution panchromatic and lower resolution multispectral imagery to create a single high resolution color image
38The Earth Observing System (EOS) is a program of NASA comprising a series of artificial satellite missions and scientific instruments in Earth orbit designed for long-term global observations of the land surface, biosphere, athmosfere, and oceans of the Earth. The first satellite component of the program was launched in 1997.Passive remote sensing: VISIBLE
39Landsat 7Landsat 7, launched on April 15, 1999, is the latest satellite of the Landstat program.Landsat 7's primary goal is to refresh the global archive of satellite photos, providing up-to-date and cloud free images.Although the Landsat Program is managed by NASA, data from Landsat 7 is collected and distributed by the USGS.The NASA World Wind project allows 3D images from Landsat 7 and other sources to be freely navigated and viewed from any angle. Landsat 7 data has eight spectral bands with spatial resolutions ranging from 15 to 60 meters.Passive remote sensing: VISIBLE
42MODIS True color (250 m resolution) Phytoplankton bloom South Atlantic Ocean (off Argentina coast)Coccolotophorids bloom in Bering Sea
43True color satellite images of Italian Seas (non-dusty and dusty cases)
44IKONOSPassive remote sensing: VISIBLEis a commercial earth observation satellite and was the first to collect publicly available high-resolution imagery at 1- and 4-meter resolution. It offers multispectral(MS) and panchromatic (PAN) imagery.Spatial resolution0.8 m panchromatic (1-m PAN Panchromatic)4-meter multispectral (4-m MS Multispectral)1-meter pan-sharpened (1-m PS Pansharpening)Spectral Resolution: Band1-m PAN4-m MS & 1-m PS1 (Blue) µm µm2 (Green)* µm3 (Red)* µm4 (Near IR)* µmTemporal resolution: the revisit rate for IKONOS is 3 to 5 days off-nadir and 144 days for true-nadir
47Advanced Very High Resolution Radiometer (AVHRR) data : Passive remote sensing: INFRAREDSea Surface Temperature (SST)NOAA (National Oceanic and Atmospheric Administration) satellitesAdvanced Very High Resolution Radiometer (AVHRR) data :5 channels in VIS & IRCloud maskingMCSST algorithm to estimate SSTThe AVHRR instrument also flies on the METOP series of satellites. The three planned METOP satellites are part of the Eumetsat Polar System (EPS) run by Eumetsat.Link:
48Sea Surface Temperature (SST) algorithm Passive remote sensing: INFRAREDSea Surface Temperature (SST) algorithmExample of an algorthmSST=A*T4+B*(T4-T5)+C*(T4-T5)*(sec(θ)-1)+DA, B, C, D = empirical coefficients specific for each satellite
49Passive remote sensing: INFRARED Sea surface temperature (SST) - is the temperature of a very thin layer of about 10 micrometres thick or skin of the ocean which leads to the phrase skin temperature (because infared radiation is emitted from this layer).Deviation of the temperature from deep undisturbed water during daylight warming. Notice logarithmic scale.Deviation of the temperature from deep undisturbed water during night. Notice logarithmic scale.
53Composite SST images of NW Atlantic SST constructed from AVHRR data Passive remote sensing: INFRAREDSea Surface Temperature (SST)Gulf StreamComposite SST images of NW Atlantic SST constructed from AVHRR data
54Altimetry Jason Links: http://sealevel.jpl.nasa.gov Active remote sensing: MICROWAVEAltimetryJasonLinks:
56Active remote sensing: MICROWAVE AltimetrySatellite altimetry can be used to measure marine geostrophic currents
57Altimetry Satellite altimetry to measure marine geostrophic currents Active remote sensing: MICROWAVEAltimetrySatellite altimetry to measure marine geostrophic currentsLinks:
58Sea Surface Height (SSH) in the Caribbian Sea cm
59Synthetic Aperture Radar (SAR) Active remote sensing: MICROWAVESynthetic Aperture Radar (SAR)SAR imaging (MW through clouds)Small gravity and capillary waves (also referred as Bragg waves) at the ocean surface reflect the radar signal.The generation of these waves is damped by thin oily layers.Imaging radars are useful for detecting oil spills or leaks from abandoned oil wells.
60Synthetic Aperture Radar (SAR) Active remote sensing: MICROWAVESynthetic Aperture Radar (SAR)Strait of Gibraltar : Surface signature of internal waves
62Synthetic Aperture Radar (SAR) Active remote sensing: MICROWAVESynthetic Aperture Radar (SAR)Gulf of Naples, Italy: Circulation structures
63Synthetic Aperture Radar (SAR) Active remote sensing: MICROWAVESynthetic Aperture Radar (SAR)Ship and its wake
64What do we sense from space that is useful for modeling Chlorophyll per unit of volume within the upper layerClear sky irradiation at the sea surface, corrected for the absorption by ozone, scattering and absorption by the aerosols, effect of clouds.Sea surface temperature from which a vertical profile is derived of a reasonable estimate of a mean value in the euphotic zone.In global application also radar altimetry is used for sea surface height, heat storage in upper ocean and nutrient storage
65Satellite versus in situ measurement: advantages and disadvantages near synoptic observationsmeasurement above to the upper optical depthsampling time interval is large once a day for the polar-orbiting, more frequent for geostationarycloud coverage interfere with measurementnot all parameters can be measuredlower accuracy and precisionIN SITUnot synoptic observationsmeasurement along the water columntime interval can be shorterclouds do not interfere with measurementall parametershigher accuracy and precision
66Remote SensingMooring and TripodsIn-situ Non-stationary Platforms
67Thanks for your attention and for your very warm hospitality