Natural-Color and Color-Infrared Image Mosaics of the 
  Colorado River Corridor in Arizona Derived from the May 
  2009 Airborne Image Collection

  By Philip A. Davis

  Data Series 780

  2013

  U.S. Department of the Interior
  U.S. Geological Survey


  Abstract:

  The Grand Canyon Monitoring and Research Center (GCMRC) of 
  the U.S. Geological Survey (USGS) periodically collects 
  airborne image data for the Colorado River corridor within 
  Arizona (fig. 1) to allow scientists to study the impacts 
  of Glen Canyon Dam water release on the corridor's natural 
  and cultural resources. These data are collected from just 
  above Glen Canyon Dam (in Lake Powell) down to the entrance 
  of Lake Mead, for a total distance of 450 kilometers (km) 
  and within a 500-meter (m) swath centered on the river's 
  mainstem and its seven main tributaries (fig. 1). The most 
  recent airborne data collection in 2009 acquired image data 
  in four wavelength bands (blue, green, red, and near 
  infrared) at a spatial resolution of 20 centimeters (cm). 
  The image collection used the latest model of the Leica 
  ADS40 airborne digital sensor (the SH52), which uses a 
  single optic for all four bands and collects and stores 
  band radiance in 12-bits. Davis (2012) reported on the 
  performance of the SH52 sensor and on the processing steps 
  required to produce the nearly flawless four-band image 
  mosaic (sectioned into map tiles) for the river corridor. 
  The final image mosaic has a total of only 3 km of surface 
  defects in addition to some areas of cloud shadow because 
  of persistent inclement weather during data collection. The 
  2009 four-band image mosaic is perhaps the best image 
  dataset that exists for the entire Arizona part of the 
  Colorado River.

  Some analyses of these image mosaics do not require the 
  full 12-bit dynamic range or all four bands of the 
  calibrated image database, in which atmospheric scattering 
  (or haze) had not been removed from the four bands. To 
  provide scientists and the general public with image 
  products that are more useful for visual interpretation, 
  the 12-bit image data were converted to 8-bit natural-color 
  and color-infrared images, which also removed atmospheric 
  scattering within each wavelength-band image. The 
  conversion required an evaluation of the histograms of each 
  band's digital-number population within each map tile 
  throughout the corridor and the determination of the 
  digital numbers corresponding to the lower and upper one 
  percent of the picture-element population within each map 
  tile. Visual examination of the image tiles that were given 
  a 1-percent stretch (whereby the lower 1- percent 12-bit 
  digital number is assigned an 8-bit value of zero and the 
  upper 1-percent 12-bit digital number is assigned an 8-bit 
  value of 255) indicated that this stretch sufficiently 
  removed atmospheric scattering, which provided improved 
  image clarity and true natural colors for all surface 
  materials.

  The lower and upper 1-percent, 12-bit digital numbers for 
  each wavelength-band image in the image tiles exhibit 
  erratic variations along the river corridor; the variations 
  exhibited similar trends in both the lower and upper 1-
  percent digital numbers for all four wavelength-band images 
  (figs. 2-5). The erratic variations are attributed to (1) 
  daily variations in atmospheric water-vapor content due to 
  monsoonal storms, (2) variations in channel water color due 
  to variable sediment input from tributaries, and (3) 
  variations in the amount of topographic shadows within each 
  image tile, in which reflectance is dominated by 
  atmospheric scattering.

  To make the surface colors of the stretched, 8-bit images 
  consistent among adjacent image tiles, it was necessary to 
  average both the lower and upper 1-percent digital values 
  for each wavelength-band image over 20 river miles to 
  subdue the erratic variations. The average lower and upper 
  1-percent digital numbers for each image tile (figs. 2-5) 
  were used to convert the 12-bit image values to 8-bit 
  values and the resulting 8-bit four-band images were stored 
  as natural-color (red, green, and blue wavelength bands) 
  and color-infrared (near-infrared, red, and green 
  wavelength bands) images in embedded geotiff format, which 
  can be read and used by most geographic information system 
  (GIS) and image-processing software. The tiff world files 
  (tfw) are provided, even though they are generally not 
  needed for most software to read an embedded geotiff image.

  All image data are projected in the State Plane (SP) map 
  projection using the central Arizona zone (202) and the 
  North American Datum of 1983 (NAD83). The map-tile scheme 
  used to segment the corridor image mosaic followed the 
  standard USGS quarter-quadrangle (QQ) map borders, but the 
  high resolution (20 cm) of the images required further 
  quarter segmentation (QQQ) of the standard QQ tiles, where 
  the image mosaic covered a large fraction of a QQ map tile 
  (segmentation shown in figure 6, where QQ_1 to QQ_4 shows 
  the number convention used to designate a quarter of a QQ 
  tile). To minimize the size of each image tile, each image 
  or map tile was subset to only include that part of the 
  tile that had image data. In addition, some QQQ image tiles 
  within a QQ tile were combined when adjacent QQQ map tiles 
  were small. Thus, some image tiles consist of combinations 
  of QQQ map tiles, some consist of an entire QQ map tile, 
  and some consist of two adjoining QQ map tiles. The final 
  image tiles number 143, which is a large number of files to 
  list on the Internet for both the natural-color and color-
  infrared images. Thus, the image tiles were placed in seven 
  file folders based on the one-half-degree geographic 
  boundaries within the study area (fig. 7). The map tiles in 
  each file folder were compressed to minimize folder size 
  for more efficient downloading. The file folders are 
  sequentially referred to as zone 1 through zone 7, 
  proceeding down river (fig. 7). The QQ designations of the 
  image tiles contained within each folder or zone are shown 
  on the index map for each respective zone (figs. 8-14).

  Disclaimer:

  Although these data have been processed successfully on a 
  computer system at the U.S. Geological Survey, no warranty 
  expressed or implied is made regarding the display or 
  utility of the data on any other system, or for general or 
  scientific purposes, nor shall the act of distribution 
  constitute any such warranty. The U.S. Geological Survey 
  shall not be held liable for improper or incorrect use of 
  the data described and (or) contained herein.

  Contact Information:

  If you have any questions regarding this dataset please 
  contact:
  Philip A. Davis, Research Geologist
  U.S. Geological Survey
  2255 North Gemini Drive, Building 4
  Flagstaff, AZ 86001
  pdavis@usgs.gov
  (928) 556-7084

  ----------------------------------------------------
  This Data Series includes the following Information: 
  ----------------------------------------------------
  DIRECTORY

  index_maps

  Colorado_River_Index_Map.pdf -- Index map stored in Adobe 
  Acrobat (PDF) format displaying the extent of the Colorado 
  River within Arizona in the geographic coordinate system. 
  Index map is also provided in jpeg format.

  Colorado_River_Image_Index_Map_Zonex.pdf -- Index map of 
  the QQ image tiles contained within each of 7 zones of 
  folders that were used to collate the image tiles. This 
  information is displayed in the geographic coordinate 
  system and stored in both PDF and jpeg formats. 

  image_files

  Twenty-centimeter (20-cm) natural-color and color-infrared 
  airborne-image mosaics in geotiff format with their tfw 
  files. All images with their tfw and metadata files are 
  compressed with standard file compression software to 
  facilitate file transfer.

  metadata

  QQQ/QQ_SP_NAD83_Z202_NC.tif.txt -- FGDC compliant metadata 
  files for each quarter-quarter-quadrangle (QQQ) or quarter-
  quadrangle (QQ) image tile. NC designates natural- color 
  image data.

  QQQ/QQ_SP_NAD83_Z202_CIR.tif.txt -- FGDC compliant metadata 
  files for each quarter-quarter-quadrangle (QQQ) or quarter-
  quadrangle (QQ) image tile. CIR designates color- infrared 
  image data. 

  shapefiles

  Colorado_River_Image_Mosaic_Index.shp -- A shapefile 
  showing the QQ image-tile and collated-tile zone boundaries 
  for the Colorado River corridor within Arizona.

  index.html -- http://pubs.usgs.gov/ds/780/

  1_readme.txt and 1_readme.pdf -- This file.

  Reference Cited:

  Davis, P.A., 2012, Airborne digital-image data for 
  monitoring the Colorado River corridor below Glen Canyon 
  Dam, Arizona, 2009--Image-mosaic production and comparison 
  with 2002 and 2005 image mosaics: U.S. Geological Survey 
  Open-File Report 2012-1139, 82 p., 
  http://pubs.usgs.gov/of/2012/1139/.

  figure illustrations are available at 
  http://pubs.usgs.gov/ds/780/1_readme/

  Figure 1. Map of the Colorado River corridor in Arizona 
  that is monitored by the U.S. Geological Survey's Grand 
  Canyon Monitoring and Research Center (GCMRC). Blue line 
  traces the course of the Colorado River; gray lines are 
  roads and trails. Blue decimal numbers are river miles from 
  Lees Ferry (river mile 0.0; river miles are negative 
  upstream of Lees Ferry); Glen Canyon Dam is at river mile 
  -16.0.

  Figure 2. Graph of the band-1 (blue wavelength) digital 
  numbers (DN) at the lower (blue points) and upper (red 
  points) 1-percent (%) population of picture elements for 
  each of the 143 image tiles relative to river mile (RM) 
  along the Colorado River corridor. The yellow and green 
  lines trace the 20-mile-average digital numbers for the 
  lower and upper 1-percent picture-element population within 
  the 143 image tiles. 

  Figure 3. Graph of the band-2 (green wavelength) digital 
  numbers (DN) at the lower (blue points) and upper (red 
  points) 1-percent (%) population of picture elements for 
  each of the 143 image tiles relative to river mile (RM) 
  along the Colorado River corridor. The yellow and green 
  lines trace the 20-mile-average digital numbers for the 
  lower and upper 1-percent picture-element population within 
  the 143 image tiles. 

  Figure 4. Graph of the band-3 (red wavelength) digital 
  numbers (DN) at the lower (blue points) and upper (red 
  points) 1-percent (%) population of picture elements for 
  each of the 143 image tiles relative to river mile (RM) 
  along the Colorado River corridor. The yellow and green 
  lines trace the 20-mile-average digital numbers for the 
  lower and upper 1-percent picture-element population within 
  the 143 image tiles. 

  Figure 5. Graph of the band-4 (near-infrared wavelength) 
  digital numbers (DN) at the lower (blue points) and upper 
  (red points) 1-percent (%) population of picture elements 
  for each of the 143 image tiles relative to river mile (RM) 
  along the Colorado River corridor. The yellow and green 
  lines trace the 20-mile-average digital numbers for the 
  lower and upper 1-percent picture-element population within 
  the 143 image tiles.

  Figure 6. Segmentation and number-designation scheme for 
  quartering U.S. Geological quarter-quadrangle (QQ) map 
  tiles when the airborne image data fill a large fraction of 
  a map tile and the image tile needed to be sectioned (into 
  QQQ image tiles) to reduce its file size. QQ_1 through QQ_4 
  are examples the numbered naming convention for QQQ map 
  tiles.

  Figure 7. Map of the Colorado River ecosystem, showing the 
  U.S. Geological Survey quarter-quadrangle (QQ) map-tile 
  scheme (green boxes) used to segment the corridor's image 
  mosaic into image tiles. The 143 QQ and QQQ image tiles 
  were collated and compressed into seven folders or zones 
  (red boxes) to facilitate internet posting and downloading 
  of the image tiles. Blue line traces the course of the 
  Colorado River; gray lines are roads and trails. Blue 
  decimal numbers are river miles from Lees Ferry (river mile 
  0.0; river miles are negative upstream of Lees Ferry); Glen 
  Canyon Dam is at river mile -16.0.

  Figure 8. Map of the quarter-quadrangle (QQ) map tiles 
  contained within zone 1 of the Colorado River corridor. 
  Blue line traces the course of the Colorado River. Blue 
  decimal numbers are river miles from Lees Ferry (river mile 
  0.0; river miles are negative upstream of Lees Ferry); Glen 
  Canyon Dam is at river mile -16.0. 

  Figure 9. Map of the quarter-quadrangle (QQ) map tiles 
  contained within zone 2 of the Colorado River corridor. 
  Blue line traces the course of the Colorado River. Blue 
  decimal numbers are river miles from Lees Ferry (river mile 
  0.0; river miles are negative upstream of Lees Ferry); Glen 
  Canyon Dam is at river mile -16.0. 

  Figure 10. Map of the quarter-quadrangle (QQ) map tiles 
  contained within zone 3 of the Colorado River corridor. 
  Blue line traces the course of the Colorado River. Blue 
  decimal numbers are river miles from Lees Ferry (river mile 
  0.0; river miles are negative upstream of Lees Ferry); Glen 
  Canyon Dam is at river mile -16.0. 

  Figure 11. Map of the quarter-quadrangle (QQ) map tiles 
  contained within zone 4 of the Colorado River corridor. 
  Blue line traces the course of the Colorado River. Blue 
  decimal numbers are river miles from Lees Ferry (river mile 
  0.0; river miles are negative upstream of Lees Ferry); Glen 
  Canyon Dam is at river mile -16.0. 

  Figure 12. Map of the quarter-quadrangle (QQ) map tiles 
  contained within zone 5 of the Colorado River corridor. 
  Blue line traces the course of the Colorado River. Blue 
  decimal numbers are river miles from Lees Ferry (river mile 
  0.0; river miles are negative upstream of Lees Ferry); Glen 
  Canyon Dam is at river mile -16.0. 

  Figure 13. Map of the quarter-quadrangle (QQ) map tiles 
  contained within zone 6 of the Colorado River corridor. 
  Blue line traces the course of the Colorado River. Blue 
  decimal numbers are river miles from Lees Ferry (river mile 
  0.0; river miles are negative upstream of Lees Ferry); Glen 
  Canyon Dam is at river mile -16.0. 

  Figure 14. Map of the quarter-quadrangle (QQ) map tiles 
  contained within zone 7 of the Colorado River corridor. 
  Blue line traces the course of the Colorado River. Blue 
  decimal numbers are river miles from Lees Ferry (river mile 
  0.0; river miles are negative upstream of Lees Ferry); Glen 
  Canyon Dam is at river mile -16.0.