1. Data Models, Pixels, and Satellite Bands

3. Understand the differences between raster and vector data. What are digital numbers (DNs) and what do they represent in remotely sensed data? What are satellite bands? Be able to define spatial and spectral resolution. What are some advantages and disadvantages of high spatial resolution? What are some advantages and disadvantages of high spectral resolution?

4. Raster Data Images are grids of cells or “pixels” Properties of each pixel are represented by a digital number (DN) A pixel represents an area on the ground Vector Data Points, lines, and areas Defined by x,y coordinates and info about “connectedness” Attributes can describe the features they represent

5. 100102500122357525559092 11212112320078200207593 187202358790 140144526889 232376566217814224531 001035576324213736250 Raster Grid w/ DNs Point Line or Arc Area or Polygon Vector Features

6. Imaginary matrix (row & column format) is placed on the feature (e.g., the ground) Some phenomenon (e.g. amount of light) is measured A value (digital number) representing the amount of light is assigned to each grid cell (pixel).

9. 3247679311 10579 35 23 11 56 43 89 21 213 245 201 179 136155 55 203 16363 211189 145 109122202

10. For remote sensing, the total amount of EMR from the area of a pixel on the ground is recorded as a digital number (DN). Depending on the intensity of the EMR, a numeric value is assigned to each pixel Low or None - Lowest value (dark or black) High - Maximum value (bright or white) Others - Scaled in between (gray)

11. Digital images are matrices of digital numbers (DNs). Satellite bands capture light from different wavelength regions. There is one layer (or matrix) for each satellite band. Each band covers the same area on the ground Each DN corresponds to one pixel in one band If there are 6 bands each pixel will be described by 6 DNs, one for each band The DNs control how a computer displays an image on your computer screen

13. Image bands are like a collection of pictures taken simultaneously of the same place, each of which measures reflected light from a different part of the spectrum. Together, image bands allow us to create spectral curves for each pixel.

14. Images are presented as 2-d grids. Each pixel (one square) has a location (x,y). Position of pixel (x,y) often described in terms of rows and columns (image coordinates) but can be translated (projected) into other coordinate systems (map coordinates, e.g., latitude/longitude, UTM, etc.) (2,3) (4,1)

15. DNs are relative measures of radiance DNs are NOT reflectance DNs can be converted to ground reflectance if you know atmospheric properties, etc. The range of DNs depends on the radiometric resolution of the recording instrument A common range of satellite DNs is 0 – 255.

18. Spatial Spectral Radiometric Temporal

19. The dimension of one side of a single pixel The extent of the smallest object on the ground that can be distinguished in the imagery Determined by the Instantaneous Field of View of satellite instruments (IFOV) Determined by altitude, camera (lens), and film characteristics for air photos.

20. 30 m Landsat pixel. Resolution? Area?

21. Finer (higher) Coarser (lower)

22. Satellites: ~ 0.3 m to > 1 km Air photos ~ 1” to coarser

23. MODIS: 250 - 1000 m Landsat MSS: 80 m Landsat TM5, 7, 8: 30 m SPOT: 20 m ASTER: 15 m IRS Pan: 5 m Worldview 3 Pan: 31 cm (!!)

24. Quickbird (Digital Globe, Inc.) ~ 2.4 m spatial resolution in multispectral bands.

25. MODIS 500 m spatial resolution

26. Zoom and Enhance! (YouTube) The Truth! Group discussion: Can you extract (zoom and enhance!) information from an image when the information is in an area smaller than a pixel?

27. How finely an instrument “divides up” the range of wavelengths in the electromagnetic spectrum How many spectral “bands” an instrument records Landsat 8 bands (in red) overlaid on plant spectral reflectance. https://landsat.usgs.gov/tools _spectralViewer.php

28. Measure the EMR across a wide range of wavelengths E.g., the visible portion of EMR Assign a single DN for sum of all visible light energy in that range hitting the sensor Analogous to black and white (panchromatic) film Called a panchromatic band

29. bluegreenred 0.40.70.60.5 UVNear-infrared

30. Measure EMR across narrower ranges E.g., Blue, green, and red bands Assign a DN for each of these wavelength ranges to create 3 bands

31. bluegreenred 0.40.70.60.5 UVNear-infrared

32. Finer (higher) Spectral Resolution RGB RedGreenBlue

33. High Spectral Resolution Low Spectral Resolution Wavelength (nm) Reflectance

35. Remotely sensed imagery are RASTER data composed of grids of pixels organized in bands (layers) Size of pixels is called spatial resolution of sensor Number of bands is called spectral resolution of sensor Digital numbers are associated with pixels and tell you relatively how much light came from that area on the ground to the satellite sensor.