Introduction to Remote Sensing

1. Introduction to Remote Sensing • Resolution • Digital Images • Image Interpretation • Satellites and Sensors

2. Remotes Sensing Technology • Remote Sensing Images can be obtained from: • Aerial Photographs • Contract a company to take the aerial photographs • Obtain from local Property Appraiser’s Office • Obtain from USGS • Satellite Images • There are a number of countries that operate satellites that collect images of the Earth for commercial purposes • LANDSAT is operated by the United States

3. Digital Images • A digital image can be broken down • layers (or CHANNELS or BANDS) representing different types of light • each layer is black and white, • combination of three channels result in a color image • into a regular grid of PICTURE ELEMENTS or PIXELS

4. Digital Images • An aerial photograph or satellite image has three different resolutions • The SPATIAL resolution • The SPECTRAL resolution • The RADIOMETRIC resolution • The TEMPORAL resolution

5. Resolution & Remote Sensing Systems 4 major resolutions associated with each remote sensing system • Spectral resolution • Spatial resolution • Temporal resolution • Radiometric resolution These resolutions should be understood by the scientist in order to extract meaningful biophysical or hybrid information from remotely sensed imagery.

6. Resolution • Resolving power • Measure of the ability of a sensor to distinguish between signals that are spatially near or spectrally similar

7. Spectral Resolution Number and size of the bands which can be recorded by the sensor – nominal spectral resolution • Course – sensitive to large portion of ems contained in a small number of wide bands • Fine – sensitive to same portion of ems but have many small bands Goal – finer spectral sampling to distinguish between scene objects and features More detailed information about how individual features reflect or emit em energy increase probability of finding unique characteristics that enable a feature to be distinguished from other features.

8. Spectral Resolution • Difficult to create detector that has extremely sharp bandpass boundaries such as describe in previous slide • More precise method of stating bandwidth is look at typical Gaussian-shape of the detector sensitivity • Describe bandwidth as Full Width at Half Maximum (FWHW)

9. Spectral Resolution • The SPECTRAL resolution defines the range of light stored in the image • A black and white photograph stores a visible light; it has one channel that stores the light for 0.4 to 0.7 micrometers • A natural color image stores reflected red, blue and green light in different channels; e.g. 0.45 - 0.52 mm for blue, 0.52 - 0.60 mm for green and 0.63 - 0.69 mm for red • A LANDSAT image contains 7 channnels as described above that store reflected light other than visible light. • A HYPERSPECTRAL image contains hundreds of channels. E.g. A hyperspectral image that collects visible light may divide the visible light range into 300 channels, each channel containing a narrow range of wavelengths.

10. Spatial Resolution • Measure of the smallest angular or linear separation between 2 objects that can be resolved by the sensor • In practice, sensor system’s nominal spatial resolution is the dimension in meters (or feet) on the ground projected instantaneous field of view (IFOV) • Generally, smaller spatial resolution  greater the resolving power of the sensor system

11. Spatial Resolution • The SPATIAL resolution defines that size of Earth’s surface that is stored in a pixel • In a LANDSAT image a pixel represents 30 m by 30 m of the Earth’s surface. • In an USGS orthophotograph a pixel repesents 1 m by 1 m of the Earth’s surface.

12. Graphic representation showing differences in spatial resolution among some well known sensors (Source: Landsat 7 Science Data Users Handbook)

14. Spatial Resolution Useful rule: To detect a feature, the spatial resolution of the sensor system should be less than ½ the size of the feature measured in its smallest dimension.

15. Temporal Resolution • How often the remote sensing system records imagery of a particular area.

16. Refers to the sensitivity of the sensor to incoming radiance. How much change in radiance must there before a change in recorded brightness value takes place. This sensitivity to different signal levels will determine the total number of values that can be generated by the sensor 26 = (0-63) 64 28 = (0-255) 256 210 = (0-1023) 1024 Examples: GOES Imager – 10bit Landsat 7 ETM+ - 8bit Radiometric Resolution

17. Radiometric Resolution • The RADIOMETRIC resolution defines the range of values that an individual pixel can have • Typical digital images have a range of values from 0 – 255 (a total of 256 possible values). • An image that just shows black or white pixels would only store 0 (black) or 1 (white).

18. Summary of Resolution • By increasing 1 or any combination of these resolutions, increase chance of obtaining remotely sensed data about a target that contains accurate, realistic, and useful information. • Downside of increased resolution  need for increased storage space, more powerful processing tools, more highly trained individuals.

19. Aerial Photography • Types depend on: • the altitude of the plane • the camera • the angle of view and • the type of film used

20. The angle of view • Vertical (directly over) • shows the scale and distance • Oblique (at an angle) • shows the object size

21. A Vertical Aerial Photograph

22. An oblique photograph

23. Photographic films • Black and White • Color • InfraRed • beyond the visible part of the spectrum

24. Monochrome(black and white)

25. Panchromatic (color)

26. Color Infrared (heat) • Used for vegetation studies • Green vegetation strongly reflects IR • Vigorously growing vegetation appears red

27. Image Interpretation • Size of objects • relative to one another • Shape • depends on the object outline • Image tone • brightness - hue, colour • Patterns • arrangement of features

28. Image Interpretation • Texture • smooth or coarse • Shadow • helps determine heights • Site • location helps recognition • Association • features that are normally found near others

29. Interpretation

30. Difficulties with Interpretation • unfamiliar prospective • viewing from above • use of wavelengths outside visible light range • Images often display different types of infrared light • Colors in image not that same as colors seen by us • E.g. False infrared images displayed reflect near infrared light using red • unfamiliar scales and resolution • Landsat image’s pixels are 30 m by 30 m • SPOT image’s pixels are 20 m by 20 m • Aerial photograph’s pixels can be smaller than 6inches

31. Characteristics of Objects • Shape • the general form of the object • stereo photographs also show height which further defines shape

32. Characteristics of Objects • Size • this needs to be considered in reference to scale • What is the object in the image • The image covers approx 1 square mile?

33. Characteristics of Objects • Pattern • this is the spatial arrangement of objects • e.g. Orchard vs. Forest • Man made objects vs. natural objects

34. Characteristics of Objects • Tone (Hue) • the relative brightness of an object or its color

35. Characteristics of Objects • Texture • frequency of tonal changes • e.g. grass appears ‘smoother’ than forest • depends on scale

36. Characteristics of Objects • Shadows are both useful and a nuisance • define the profile of the object • hide objects in the shadow area

37. Characteristics of Objects • Site • topographical location • e.g. palm trees are not found in New England • Association • what objects are found together • e.g. a Ferris wheel

38. Strategies • Other information in addition to the image • e.g. for crop identification use information on typical planting dates, recent weather conditions etc

39. Strategies • There are two types of Interpretation keys. • Selective keys provide a set ofexample images. • E.g. pictures of different trees from above • Elimination keys makes the interpreter make a series of decision. • Is the ‘crown’ of the tree large or small: small might suggest pine tree in a given location rather than oak trees. • better for man made objects rather than vegetation.

40. Strategies • Consider film / filter combinations (or sensor channels) • Would a false infra red image be better than a natural color image? • Consider the Arial extent of the photograph • Do you need to have great detail or large aerial coverage?

41. Approaching Classification • Define the classifications. • What objects are you trying to identify in the image • What objects are considered the same • Pine tree forest and oak tree forest considered as just forest? • ‘fuzzy’ edges, • Try to give good definition of where boundaries lie between natural objects • E.g. where desert ends and non-desert starts

42. What is a satellite? • The term Satellite simply refers to a body in orbit around another body. • In 1957 the first artificial satellite SPUTNIK, was launched by the Soviet Union. Today there are hundreds of these spacecraft in orbit around the Earth. • Satellites may serve many different purposes; they may be part of a television or telephone network or they can carry instruments to investigate the Earth’s surface or the Earth’s atmosphere. • Other spacecraft point towards the Sun and monitor this star, or travel for many years carrying probes or landers which investigate the atmosphere, moons or surface features of distant planets. • There are also manned spacecraft such as the US shuttle spacecraft and space stations such as MIR, the Soviet space station launched in 1986.

43. Satellite Orbits • Satellites generally have either polar orbits or geostationary orbits.

44. Meteosat • A program sponsored by 17 European weather services. It started with the successful launch of METEOSAT 1 in 1977 and has continued unabated. METEOSAT 7, the last in the current series was launched in early September 1997. • They are stationed above the equator at 0° longitude above the Gulf of Guinea and image this part of the globe every 30 minutes in three wavebands. These are: • the visible (0.4 to 1.1 micrometers), • the water vapour (5.7 to 7.1 micrometers) and • the thermal infrared (10.5 to 12.5 micrometers). • The first has a resolution of 2.5 km The first has a resolution of 2.5 km at the sub-satellite point (SSP) while the two infrared wavebands both have one of 5 km.

45. NOAA (National Oceanic & Atmospheric Administration) Polar Orbiters • The programme that started with the successful launch of TIROS-1 in 1960 continues today with the NOAA polar orbiters. The satellites' AVHRR instruments image the planet in five bands: • 8 to 0.68 micrometres • 0.725 to 1.10 micrometres • 3.55 to 3.93 micrometres • 10.30 to 11.30 micrometres • 11.50 to 12.50 micrometres

46. Geostationary Operational Environmental Satellites (GOES) • This NOAA series of geostationary weather satellites began in 1974 and continues today with the launch of a new ‘GOES-NEXT series of more advanced satellites in 1994. • The resolution varies from 4 to 8 km. • They have five wavebands: • 0.55 to 0.75micrometres • 3.80 to 4.00 ” • 6.50 to 7.00 “ • 10.20 to 11.20 ” • 11.50 to 12.50 "

47. The Space Shuttle • The space shuttle is a manned spacecraft mission, carrying astronauts and scientists as well as instruments. • The most important sensors that have been carried on the Shuttle for Earth imaging are: • The Shuttle Imaging Radar • The Metric Camera. • The Large Format Camera (LFC) • The Modular Optical-Electronic Multispectral Scanner (MOMS).

48. LANDSAT Satellite Series • First LANDSAT satellite launched in 1972 • Lasted until 1978 • Six Landsat satellites to date • LANDSAT-4 and -5 still operational • LANDSAT -6 experienced launch failure

49. Technical Information • Landsat 4 (launched 16.07.82) • Landsat 5 (launched 01.03.84) • Orbit • near polar sun-synchronous • complete orbit every 99 mins • Altitude - 705 km, 438 miles • Re-visit - 16 days

50. Landsat 1, 2 and 3 • Landsat was the first satellite to be designed specifically for observing the Earth’s surface. • Landsat 1, 2 and 3 carried a multispectral scanner (MSS) system which records reflected energy from the Earth’s surface or atmosphere across four wavebands; three visible channels and one near infrared. • The MSS has a pixel resolution of 80 metres.