Introduction to Remote Sensing Fundamentals of Satellite Remote Sensing. Mads Olander Rasmussen

Transcription

1 Introduction to Remote Sensing Fundamentals of Satellite Remote Sensing Mads Olander Rasmussen

2 01. Introduction to Remote Sensing DHI

3 What is remote sensing? the art, science, and technology of obtaining reliable information about physical objects and the environment, through the process of recording, measuring and interpreting imagery and digital representations of energy patterns derived from noncontact sensor systems. (Cowell 1997) Satellite remote sensing refers to the reception, preprocessing and later analyses of data obtained from Earth orbiting satellites (Campbell, J.B., 2001) Other terms: Earth Observation

4 Components of a remote sensing system Remote Sensing Platform PRE-PROCESSING IMAGE ANALYSIS END USER INFORMATION

5 Historical development of remote sensing systems Plane Meteorological Satellites Space Shuttle UnitedSsatte ERS-1 Commercial Satellites Sputnik Balloon Pigeon camera Landsat-1 Landsat-4 Space Station Space Program

6 Historical development of remote sensing systems Landsat Quickbird NOAA AVHRR

7 Other sources of Remote Sensing data Airborne (lidar, hyperspectral, thermal etc.). Unmanned (UAV) Ground sensors

8 but focus of this course is Satellite Remote Sensing

9 02. The fundamentals DHI

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11 Key parameters Satellite and Sensor types Satellite orbit Spatial resolution Temporal resolution Spectral resolution From reflected light to a satellite image The electromagnetic spectre Spectral signatures Digital image processing

12 Satellite orbits Polar-orbiting satellites ( km) Most satellites are polar orbiting. They circle the Earth in a certain track that allows them to monitor all areas within a certain time interval (e.g. Landsat, SPOT, WorldView, Sentinel) Geo-stationary satellites (36000 km) Geo-stationary satellites orbit Earth in app km altitude. Monitors the same area of the Earth at all times (e.g. Meteosat, NOAA GOES)

13 Satellite orbits Video

14 Types of Satellite Sensors Passive Sun s energy which is reflected (visible) or Absorbed and re Absorbed and re-emitted as emitted as thermal infrared wavelengths Landsat, SPOT, WorldView, Pleiades Active Emit radiation Radiation reflected is detected and measured SAR, LIDAR, and SONAR SRTM (Shuttle Radar Topography Mission)

15 There is no such thing as bad weather Passive/ Optical data Active/ SAR data An image type for all weather conditions: DHI

16 Very High Resolution Ikonos (1 / 4 m) QuickBird (0,6 / 2.4 m) WorldView-1 (0,5 m) 2007 GeoEye-1 (0,5 / 2 m) WorldView-2 (0,5/2 m) 2009 Pleiades (0,5/2 m) 2011/2012 SkyBox etc!

17 High/Medium Resolution Landsat (15-90 m) SPOT ( m) IRS (5 23 m) Aster (15-90 m) 1999 RapidEye (5 m) 2009 DMC2 (22m) SPOT 6-7 (1.5m) 2012/2014 Sentinel 2 (10/20/60m) PlanetLabs (5-8m)

18 Low Resolution NOAA AVHRR (1 km) MODIS ( m) MERIS ( m) 2002 NPP VIIRS (750m) Geostationary (Meteosat/MSG/GOES,MTSAT etc) (3km 8 km)

19 Getting access to imagery with high resolution A. Archive imagery On/offline archives What has been imaged in the past B. New acqusition Possibility of controlling the time and area to be imaged Area of 2400 sqkm can be collected in a few minutes! DHI

20 Key parameter: RESOLUTION Spatial is defined as the area of ground represented by one pixel in the image Temporal is defined as the frequency at which images are recorded in a specific place on the earth Spectral is a measure of the number (and width) of bands in which a given sensor records information

21 Key parameter: RESOLUTION Spatial is defined as the area of ground represented by one pixel in the image Temporal is defined as the frequency at which images are recorded in a specific place on the earth Spectral is a measure of the number (and width) of bands in which a given sensor records information

22 Digital Image The registered energy for every band is written to an image file; every observation becomes a pixel value. Each value represents the average brightness for a portion of the surface, represented by the square unit areas in the image. In computer terms the grid is commonly known as a raster, and the square units are cells or pixels Satellite Images are typically stored as GeoTiff images (.tif)

23 Spatial Resolution

24 Spatial Resolution Very High Resolution m High/Medium Resolution m Low Resolution 250 m 8 km

25 Spatial Resolution Spatial resolution is controlled by the specifications of the radiometer, view angle geometry and the orbit altitude

26 Spatial Resolution - Landsat 8

27 MODIS (250m)

28 Balance between coverage and resolution

29 MODIS vs. Landsat

30 Landsat (30m)

31 Landsat (30m)

32 Landsat (30m)

33 VHR (50cm)

34 VHR (50cm)

35 VHR (50cm) vs Landsat (30m)

36 Landsat (30m)

37 Balance between coverage and resolution

38 Key parameter: RESOLUTION Spatial is defined as the area of ground represented by one pixel in the image Temporal is defined as the frequency at which images are recorded in a specific place on the earth Spectral is a measure of the number (and width) of bands in which a given sensor records information

39 Around the world in 90 minutes 24h 48h

40 Around the world in 90 minutes

41 Temporal Resolution Temporal resolution is important when choosing imagery If the goal is to monitor a process that changes rapidly (e.g. floods, fires), several images may be needed per day If the goal is to document a slow process (e.g. Vegetation trends, Glacier movement or urban growth) then one image per year would suffice

42 Importance of time series Use time series of satellite data to include seasonal variations of wetness/flooding

43 Importance of time series

44 Importance of time series

45 Key parameter: RESOLUTION Spatial is defined as the area of ground represented by one pixel in the image Temporal is defined as the frequency at which images are recorded in a specific place on the earth Spectral is a measure of the number (and width) of bands in which a given sensor records information

46 The electromagnetic spectre 2 relevant parts of the electromagnetic spectrum: Visible-IR (Optical) Microwave (SAR) Not all parts of the spectrum are transparent Electromagnetic radiation blocked primarily by: water vapour, Ozone, CO2 and aerosols (dust etc.)

47 Digital Colour Image

48 QB Pan Pan-cromatisk billede False-color image MS Spectral resolution WV1 Pan WV2 QB Pan Pan MS MS Blue Green Red Near-Infrared WV1 Pan Wavelength (nm) WV2 Pan MS Wavelength (nm)

49 Radiation principles Optical remote sensing is based on the detection of reflected and emitted energy at different wavelenghts Different materials will have varying reflective/emmissive proportions at different wavelengths.

50 Landsat bands 7 and 8

51 Landsat 8 - Band Combinations Natural Color False Color (urban) Color Infrared (vegetation) Agriculture Atmospheric Penetration Healthy Vegetation Land/Water Natural With Atmospheric Removal Shortwave Infrared Vegetation Analysis 6 5 4

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56 Image Classification

57 Image Classification

58 Image Classification

59 Image Classification

60 Spectral signatures

61 Reflectance (%) Blue Green Red Near-infrared Mid-infrared Spectral signatures 50 Soil Vegetation Wavelength (µm)

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63 Vegetation Index E.g. NDVI

64 NDVI?

65 NDVI

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69 Key parameter: RESOLUTION Spatial is defined as the area of ground represented by one pixel in the image Temporal is defined as the frequency at which images are recorded in a specific place on the earth Spectral is a measure of the number (and width) of bands in which a given sensor records information

70 Key parameter: RESOLUTION Radiometric refers to the effective bitdepth of the sensor (number of grayscale levels) Economic what is the cost?

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