A22EM3 Environmental Mapping

1. A22EM3 Environmental Mapping Exam Format and Revision

2. Exam Format • Exam will be in TWO sections • Part A will consist of “short answer” type questions relating to definitions and factual knowledge. All questions will be compulsory and will account for 30% of the total exam mark • Part B will consist of “essay” type questions that will require you to relate “facts” to applications and show your general understanding of the subject area. You will have a choice of TWO questions from FOUR. Part B will account for 70% of the Exam Mark.

3. Revision • The following slides will hopefully emphasise the key aspects of the series of lectures. I have also made reference to the chapters of Lillesand & Kieffer and the web based NASA tutorial which I would recommend everyone to look at.

4. Basic Concepts • What is remote sensing? Understand the concepts of “viewing” an object from a distance in the general sense. That is • It must be possible for some characteristic to be measured through the intervening medium. • This usually involves the measurement of the changes in some form of ENERGY. • The fact that different objects affects the energy in different ways can be used to characterise some property of the object

5. Components of a Sensing system • Suitable form of energy which can pass through the intervening medium • A platform to contain the appropriate measurement instruments • An instrument to sense the energy after it has interacted with the object • Data processing and analysis • Evaluation and application by the user

6. Particular Application • In Earth sensing one is interested in remote sensing through the Earths atmosphere (or oceans) • The energy used is often Electromagnetic radiation (EM) • Fundamental concepts of wavelength and amplitude (energy) • This energy can be derived form the sun (passive) or generated by the instrument (active such as radar or sonar)

7. Concepts of Energy • The sun emits a range of wavelengths with different strengths – we call this the EM spectrum. • Understand the range of the EM spectrum as generated by the sun – from visible-> IR -> Microwaves. • Remember the key names for the important wavebands.

8. Passage of EM through the Atmosphere • A range of effects which modify the EM spectrum from the sun. These affect different wavelengths in different ways and so change the form of the SPECTRUM. • Scattering (from particles in the atmosphere) • Absorption (from chemicals in the atmosphere)

9. Spectral Windows • A vital concept when one considers the best wavelengths to use • Remember which bands can pass through the atmosphere relatively unaffected.

10. Energy Interaction with a Surface Feature • Again a vital component of understanding remote sensing. • If the object changes the spectrum in some characteristic way then we can use this to identify the object. (When we look at a view of the Earth how do we decide what is ocean and what is land?)

11. Possible Interactions • Reflection • Absorption • Re-emmision THESE CAN ALL BE WAVELENGTH DEPENDENT AND SO CHANGE THE SPECTRUM

12. Use of Variation in Reflection Properties • Spectral Reflectance • Variation in % reflection with wavelength • Spectral Signature • Identification of a feature through its characteristic reflectance properties at different wavelengths.

13. Re-Emission • A special case is the study of the re-emission of radiation energy from a body. The most important is what is termed THERMAL infra red. • These are relatively long wavelength (8-14 microns) due to the temperature of the body. • They are thus key in measuring temperature, but also are useful because different objects will emit “heat” to different degrees.

14. Ground Truthing • It is possible to use theory to understand how different objects will react to EM radiation, however responses can be so diverse that further evidence that a feature can be identified is needed. This gives rise to • GROUND TRUTHING – the cross checking and validation of remote sensed data with data achieved in particular areas.

15. Instrument Platforms • Static – Stay in one area and so have limited coverage (Binocular?) • Moving – these allow larger areas to be monitored. The main methods for earth sensing are: • Airborne • Satellite

16. Satellites • Satellite Orbits (know the properties/ differences of each) • Geostationary • Polar • Orbital period (relates to height) • Repeat period (relates to recurrence of coverage over a particular area) • Remember examples of satellites types available (eg Landsat, Geos etc)

17. Special Satellite Terms • Geostationary • Inclined orbit • Sun Synchronous orbit • Orbital Period • Ground Track

18. Instruments • Fundamental characteristics needed to understand the operation of an instrument • Ground Resolution • Frequency (wavelength) resolution • Sensitivity to a particular wavelength (or band of wavelengths)

19. Important Instruments • Cameras: views of Earth in visible and IR • Mappers (have a limited series of bands to which they are sensitive) • Sounders – analyse absorption characteristics of chemical components within the atmosphere. • Radiometers – more sophisticated mappers that usually have narrower bandwidths and can more accurately measure the intensity of the reflected\wavelength.

20. Remember the basic characteristics of a mapper in terms of its bands (say Landsat bands from visible to Thermal IR) • These relate to known SPECTRAL WINDOWS

21. Combination of Instrument and Satellite • To understand the way in which an instrument covers the Earth it is important to understand the effect of the satellite orbit. • The instrument has a maximum width of coverage – the SWATH WIDTH. (185 km for Landsat (1500- 2800 km for SeaWIFS) • For this reason there may be a some time between the satellite viewing the same ground area.

22. Examples • Landsat – Swath width 185 km, but in a 100 min orbit the Earth moves about 2500 km, so it takes 16 days before Landsat is again over the same point (the REPEAT PERIOD) • SeaWifs can have a swath width up to 2800 km – thus it may have a view of the same area every orbit.

23. Image Processing and Data Analysis • Concepts of a digital picture • Pixel – smallest areas on the image which can be separated from another • An image is made up of an (x,y) array of pixels which correspond to an area on the ground • Digital Number relates to intensity of radiation in a particular pixel • For multiband systems there must be a separate array for each band and this leads to huge amounts of data.

24. Correction of Image geometry • It is possible to correct for “distortion” due to satellite motion. • The array is also “mapped” from the digital array to a conventional map coordinate system.

25. Image Enhancement • The information content of an image can be improved through digital enhancements • Contrast enhancement (histogram stretching) • False colour. The ”image” produced by the sensor is presented as a combination of red/green blue for better visualisation (thus band 1 might be red, band 3, green and band 5 blue) • Noise removal • Low frequency filtering (to look at broad features) • High frequency filtering (to look at sharp linear features)

26. Multi Image Processing • Using the information from two or more bands to improve information retrieval • Spectral “ratioing” – useful when there is uneven illumination across the scene. • Principle component analysis – reduces redundancy (didn’t cover this in lectures)

27. Image Classification • A vital link between the measuring technology and the user. A method of relating the image information to the feature at a particular point on the ground. • Supervised classification – a range of DN’s from a band can be associated with a particular known feature and these are then used to “train” the analysis programme. • Unsupervised – the computer looks for “clusters” of similar DN’s and then the user tries to relate these to actual features.

28. Radar • Advantages and disadvantages • Radar Bands – transparency to rain (or not) • Distance measurement (Ranging) though “time of flight”. i.e. measuring how long it takes a pulse of microwave energy to go from instrument to the object and back. • How a RADAR image is formed • Response of different materials to RADAR • Analysis of object by its effect on “pulse shape”

29. LIDAR • Same idea as radar but using a pulse of light. • LIDAR bathymetry – how is the water depth measured using the pulsed light? • Use for examining canopy cover

30. Sounders • Examines absorption spectrum of EM radiation coming through atmosphere • Can determine chemical composition and concentrations • Temperatures • Pressures • Vertical Sounder and Limb sounder

31. The Atmosphere • The needs for remote sensing • Key issues • Large scale phenomenon (weather systems, storm tracking) geostationary are good since they have a constant view of the same area. • Smaller scale – polar orbiting – they are lower and have better spatial resolution

32. Quantities of Interest • Weather systems and fronts, storms, cyclones etc. • Cloud properties (temperature, height, density, vapour content) • Surface temperature • Global radiation • Planetary ALBEDO • Atmospheric components (Ozone, “green house gases”/ particulates)

33. The Land • Lansat as one of the key providers of information on land features and resources • Coverage • Mapper bands and uses

34. Geological Features (Geomorphism) • Geological feature mapping • Visual and radar “textures” of surface features • Reflectance and emission of rocks – SPECTRAL SIGNATURE • Thermal inertia measurements • Radar: Returned signal depends • on roughness (terrain geometry) • Electrical properties (rock type)

35. Vegetative Features • Reasons for spectral signature of vegetative matter (and how it varies with plant health) • Great dependency on visible and near infrared so… THE NORMALISED DIFFERENCE VEGETATION INDEX (NDVI) • Why can it differentiate vegetation from rocks etc?

36. Application • Agricultue • Land use (urbanisation/ tree felling) • Plant Biomass • Plant Health • Natural Habitat • Classification of habitat • Change in habitat • Drought, Fire • Prediction of pest borne diseases, tracking and control

37. The Oceans • Key issues of features that can be analysed using RS • Review of “particular” instruments/ platforms for ocean observation • Difference in characteristics (resolution mapper bands and radar analysis) between ocean systems and land systems

38. Applications • Sea levels (topography) Satellite altimetry • Wind velocity and direction • Ocean Currents • Sea surface temperatures • Ocean Colour (various examples) NDVI! • Analysis of ocean water masses • Sea ice • Animal Tracking

39. References for each Topic Area L&K = Lillesand and KiefferNASA tut = http://rst.gsfc.nasa.gov/Front/tofc.html

40. Basic concepts L&K chapter 1 NASA tut Introduction: Theoretical, Technical and Historical Perspectives of Remote Sensing Satellite systems L&K chapter 6 NASA tut as above Image Processing L&K chapter 7 NASA tut Section 1

41. Radar L&K chapter 8 NASA tut Section 8 Thermal Sensing L&K chapter 5 NASA tut Section 9 Geological Appications NASA tut Sections 2 & 5

42. Vegetation NASA tut Section 3 Land Use NASA tut Section4 Ocean Use NASA tut Section 14