Non-photographic Remote Sensing, Digital Data Acquisition. And. Landsat Satellite Imagery. March 17, 2015

Transcription

1 Non-photographic Remote Sensing, Digital Data Acquisition And Landsat Satellite Imagery March 17, 2015

2 NON-PHOTOGRAPHIC SYSTEMS Remote Sensors all instruments that detect and measure reflected and/or emitted electromagnetic energy from a distance (recording device is NOT in contact with the objects under study) Imaging Systems collect remotely sensed data from which twodimensional pictorial representations of the objects under study can be made photographic camera and film non-photographic: multispectral scanners (passive) passive microwave RADAR and LIDAR (active) Sonar (active)

3 ELECTROMAGNETIC RADIATION interactions with the atmosphere

4 CLASSIFICATION OF NONPHOTOGRAPHIC REMOTE SENSORS PASSIVE ACTIVE

5 CLASSIFICATION OF NONPHOTOGRAPHIC REMOTE SENSORS PASSIVE ACTIVE DIGITAL CAMERA VIDEO CAMERA MULTI- SPECTRAL SCANNERS MICROWAVE SAR (Radar) LASER (Lidar) THERMAL (e.g. TIMS) VISIBLE & NIR HYPERSPECTRAL (e.g. AVIRIS) ACROSS TRACK (sweep) e.g. Landsat 5 (TM), AVHRR ALONG TRACK (push) e.g. SPOT, Landsat 8 (OLI)

6 PHOTOGRAPHIC VS. NON-PHOTOGRAPHIC not a photograph!

7 Digital Image Sources Use of digital raster images instead of photographs sources of digital photographs: digitized photographs and orthophotos digital cameras electro-optical scanners (e.g., multispectral scanners) Other digital satellite imagery (thermal, Radar, Lidar

8 Digital Satellite Image (Landsat) Aerial Photograph scan digitized

9 National Agriculture Imagery Program (NAIP) Ortho- Photography Leaf-on meter resolution U. Maine Campus

10 NON-PHOTOGRAPHIC SYSTEMS Digital Cameras use camera body and lens but the image is recorded by a Charged Coupled Detector (CCD) array rather than film electronic signals are stored digitally (pixel by pixel, band by band) on computer disks or other digital media sometimes called digital photography but not photography in the traditional sense (e.g. using film). Small format usually 35mm or 70mm. B/W or color example: Kodak Professional DCS 460 ADAR System 5000

11 Photographic Film vs. Digital Images Ground area covered in a digital image, from a digital camera, depends on sensor flying height, the instantaneous field of view (related to beta angle of optical system) and on the size of the twodimensional array (number of rows and columns of pixels) and pixel resolution No single number can represent the number of pixels a photographic image would have, if it had pixels the pixels in a CCD array are uniform in size and shape and are arranged in a systematic geometric pattern (2-D array) Silver halide grains in a photographic image are random in size, shape, and spatial distribution Generally, images on photographic film have been more detailed than digital images; although digital cameras are approaching the resolution of photographic film For every two-fold increase in resolution, there is a four-fold increase in the data storage capacity required

12 Instantaneo us Field Of View (IFOV) (H h)

13 DIGITAL IMAGING - Some Advantages Even though they usually offer poorer resolution and are more complex (and hence more expensive), non-photographic imaging systems offer several advantages over photographic cameras: operate in portions of the EMS within and beyond the wavelength sensitivities of photographic film digital output signal can be transmitted via radio telemetry and computer links and stored on magnetic tape and computer disks renewable detection process (in contrast to photographic systems in which film is both detector and storage medium) CCD elements have a wider dynamic range than film emulsion (better able to sense subtle scene radiance changes) digital data readily available for digital processing, manipulation, and integration with GIS and other computer-based tools

14 Digital Image Acquisition sensor s instantaneous field of view As the sensor sweeps across the track of the satellite, energy is recorded as a series of pixels along a scan line.

15 A digital image is composed of pixels geographically ordered and adjacent to one another. The pixels provide a continuous representation of the earth s surface. Each pixel represents a certain surface area on the ground, and provides a measure of the intensity of spectral response recorded over that unit of surface area the spectral response is recorded as a numeric value (a digital number or DN ).

16 Relationship of digital numbers and brightness levels on an eight bit, black and white or gray scale image

17 MULTISPECTRAL SATELLITE IMAGERY A multispectral image is composed of 'n' rows and 'n' columns of pixels in each of two or more spectral bands. There are in reality more than one "data set" which makes up one image. These different data sets are referred to as spectral bands, channels, or layers.

18 Landsat 8

19 Landsat - 4, 5, 7, 8 Orbital Characteristics sun-synchronous, near polar orbit: Landsat always passes over same location at same local time (8:30-10:00) orbital period = 99 min. (14.5 orbits per day) swath width = 185 km revisits the same location every 16 days (22 repeats per year)

20 Operational Land Imager (OLI) Landsat Data Continuity Mission (LDCM) Bands Wavelength (micrometers) Band 1 - Coastal aerosol Band 2 - Blue Band 3 - Green Band 4 - Red Band 5 - Near Infrared (NIR) Band 6 - SWIR Band 7 - SWIR Band 8 - Panchromatic Band 9 - Cirrus Band 10 - Thermal Infrared (TIRS) Band 11 - Thermal Infrared (TIRS) Resolution (meters) Worldwide Reference System-2 (WRS-2) path/row system Sun-synchronous orbit at an altitude of 705 km (438 mi) 233 orbit cycle; covers the entire globe every 16 days (except for the highest polar latitudes) Inclined 98.2 (slightly retrograde) Circles the Earth every 98.9 minutes Equatorial crossing time: 10:00 a.m. +/- 15 minutes

21 OLI Bands and Spectral Response

22 Landsat - 4, 5, 7, 8 Image Characteristics Worldwide Reference System (WRS) - 8 scenes over Maine Imagery archived and catalogued by USGS EROS Data Center (Sioux Falls) Scene location indexed by path / row system Paths run roughly north/south Rows run roughly east/west Scene size is ~185 x 185 km Pixel size is 30 x 30 m (~1/4 acre)

23 Comparison ETM+(L7) to OLI/TIRS (L8)

24 Comparison ETM+(L7) to OLI/TIRS (L8)

25 NON-PHOTOGRAPHIC SYSTEMS Advantages of along-track (push broom) scanners linear arrays afford longer residence time for which to measure energy from each ground resolution cell, resulting in a stronger signal fixed relationship of CCDs along each scan line results in improved geometric integrity CCDs small in size and require less power for operation w/o moving parts (e.g. oscillating mirrors), a linear array system has a higher reliability and longer life expectancy

26 SATELLITE IMAGE INTERPRETATION Manual (visual) Interpretation i.e. by a human interpreter imagery displayed in a pictorial or photograph-type format, or a digital image on a computer screen Digital Image Processing and Land Cover Classification enhance data as a prelude to visual interpretation automatically identify targets and extract information supplement and assist the human analyst

27 Landsat 8 Operational Land Imager Band 2 (blue) Band 3 (green) Band 4 (red) Band 5 (Near-IR) Band 6 (Mid-IR) Band 7(Mid-IR)

28 Red- Green Blue = Primary colors R R+G = Yellow G R+ G + B R+B = Magenta G + B = Cyan B

29 SATELLITE IMAGE INTERPRETATION (Additive Color Theory) The additive primaries: red, green, and blue (physics of light) Characteristics: No single primary can be formed by a combination of the other two. All other colors are created by mixing these three. Equal proportion of two primary colors gives complimentary colors (cyan, magenta, and yellow). Equal proportions of the three additive primaries combine to form white light.

30 LANDSAT COLOR COMPOSITES urban, pasture WHITE high high high no change, hig forest BLACK low low low no change, low Additive Color Theory and RGB Color Composites Simplified Interpretation Computer Display: RED GREEN BLUE Interpretation Image Color LAYER1 LAYER2 LAYER3 forest canopy regrow regrow regrow regrow BLUE low low high cleared before CYAN low high high cleared before GREEN low high low cleared before RED high low low cleared no regrow MAGENTA high low high cleared YELLOW high high low cleared 95-97

31 OLI band 4 (visible red) Red color write function of computer monitor OLI band 3 (visible green) OLI band 2 (visible blue) Green write function Blue write function A true color composite (RGB-432) Landsat 8 OLI

32 true color composite RGB-432 CIR false color composite RGB-543 false color composite RGB-564 Landsat 8- OLI

33 1988 Landsat Thematic Mapper (RGB-453) Same as RGB-564 color composite in Landsat 8 image Mixed Water, wetlands, clouds are masked from the imagery, and appear black Softwood dominant Hardwood dominant Harvest, Harvest,