North American Landscape Characterization (NALC) Tape Product README
Table of Contents
- 1.0 Tape Organization
- 1.1 File Structure
- 1.2 File Descriptions
- 2.0 Background
- 3.0 Data Set Characteristics
- 4.0 Procedures
- 4.1 NALC Triplicate Processing Steps
- 5.0 Restrictions
- 6.0 USGS Contact
- 7.0 References
- 8.0 Appendices
- 8.1 Sample Image Metadata
- 8.2 Metadata Field Descriptions
- 8.3 Sample Data Descriptor
- 8.4 NALC Tape Mapper File Order and File Descriptions
- 8.5 Sample NALC Tape Mapper
- 8.6 Retrieving Tape Files Using Unix "DD"
- 1.0 Tape Organization
- 1.1 File Structure
- The tape header consists of one flat file containing an ASCII-format NALC README file
and multiple metadata files.
- 1.2 File Descriptions
- See the Appendices.
- 2.0 Background
The North American Landscape Characterization (NALC) project is a component of the
National Aeronautics and Space Administration (NASA) Landsat Pathfinder Program.
Pathfinder projects focus on the investigation of global change while utilizing remote
sensing technologies. The NALC project is a cooperative effort between the U.S.
Environmental Protection Agency (EPA), the U.S. Geological Survey (USGS), and NASA to make
Landsat data available to the widest possible user community for scientific research and
general public interest. The NALC project is principally funded by the EPA Office of
Research and Development's Global Warming Research Program (GWRP) and the USGS' Earth
Resources Observation Systems (EROS) Data Center. The objectives of the NALC project are
to develop standardized remotely sensed data sets and standard analysis methods in support
of investigations of changes in land cover; to develop inventories of terrestrial carbon
stocks; to assess carbon cycling dynamics; and to map terrestrial sources of greenhouse
gas (CO, CO2, CH4, and N2O) emissions (Lunetta and Sturdevant, 1993).
- 3.0 Data Set Characteristics
The NALC project includes Landsat multispectral scanner (MSS) data acquired in the
years 1973, 1986, and 1991, plus or minus one year, with geographic coverage including the
conterminous United States and Mexico. The specific temporal windows vary for geographic
regions based on the seasonal characteristics of the vegetation cover. The NALC triplicate
scenes are geographically referenced to a 60- by 60-meter Universal Transverse Mercator
(UTM) ground coordinate grid.
- 4.0 Procedures
- 4.1 NALC Triplicate Processing Steps
- The process of generating the triplicates involves a multi-stream approach. The 1980's
image is precision corrected and registered to a map base using a three-step approach and
is used as the cartographic base to which the 1970's and 1990's data are registered. A
relational data base has been developed and maintained, which contains the corner
coordinates and quadrangle names for United States 1:24,000-scale topographic maps. This
data base was augmented with similar information for the 1:250,000- and 1:50,000-scale
topographic maps for Mexico acquired from the Instituto Nacional de Estadistica, Geografia
e Informatica (INEGI) in Aguascalientes, Mexico. The latitude and longitude coordinates of
the 1980's scene to be used for a given triplicate are intersected with the map data base
to identify the topographic maps which fall within that particular Landsat Worldwide
Reference System-2 (Landsats 4 and 5) path/row.
- The 1980's image is precision corrected and registered to a map base. In rare
situations, multiple 1980's images are used to produce a cloud-reduced composite. The
registration entails the selection of image and planimetric source control points for use
in developing the model for precision correction. Control point sources used include
1:100,000-scale USGS digital line graph (DLG) data and 1:24,000-scale USGS topographic
maps for triplicates within the United States, and 1:50,000-scale maps for triplicates
outside of the conterminous United States. The DLGs are components of the National Digital
Cartographic Data Base (NDCDB) and are comprised of the various thematic layers (e.g.,
transportation, hydrography, hypsography, political boundaries) depicted on the
1:100,000-scale topographic map series (USGS, 1989). For triplicates within the United
States, the DLG data are the primary source for control point selection. The DLGs are
interactively overlain onto the imagery to facilitate visual correlation of area features
between the imagery and the DLG data. Once a feature match has been identified, the image
(line, sample) and DLG (latitude, longitude) coordinates for a specific point along the
feature are extracted and compiled in a control point file Approximately 30 to 35 points
are extracted.
- The next step in triplicate generation involves mosaicking the digital elevation model
(DEM) data and transforming the DEM data's original geographic projection to a UTM
projection. The DEM data used in the NALC project are derived from Defense Mapping Agency
(DMA) Level-1 Digital Terrain Elevation Data (DTED) (USGS, 1987), which were digitized
from the standard National Topographic Map Series 1:250,000-scale maps. These maps provide
complete United States coverage. The DEM data, often referred to as the 3-arc-second DTED
data, are available as gridded files corresponding to 1-degree-latitude by
1-degree-longitude blocks. These blocks are mosaicked by path/row, then projected and
resampled to 60- by 60-meter pixels in a UTM projection.
- Elevation values for the ground control points are retrieved from the DEM data. The
ground control points containing X, Y, and elevation values are corrected for relief
displacement. The relief-corrected control points are then used to compute the
coefficients for a second order polynomial model that is used to geometrically correct and
reproject the 1980's MSS image to a UTM ground control coordinate system. Using cubic
convolution, the image is rectified and resampled to a UTM-projected output image
comprised of 60- by 60-meter pixels. As of July 28, 1994, a full terrain correction is
also applied to the 1980's image by correcting for the effects of relief displacement on a
pixel-by-pixel basis using the previously created DEM image.
- A verification of registration quality is performed using control points selected from
either 1:24,000-scale maps or 1:100,000-scale DLG source material. Selection of 12 to 15
verification control points proceeds in a manner similar to the selection of registration
points. Scenes must meet quality objectives of total Root Mean Square Errors (RMSEs) of
less than 1.0 pixel for United States scenes, and total RMSEs of less than 1.5 pixels for
Mexican scenes (where control sources are less reliable). Registration control points are
reselected for scenes which fail to meet quality objectives.
- The final geocoded 1980's component for each triplicate is a six-band image. Bands 1
through 4 are comprised of MSS bands 1 through 4, band 5 (an NDVI computed from MSS bands
2 and 4), and band 6 (a pixel-identity band in which pixel values greater than or equal to
1 correspond to valid image data and pixel values of 0 correspond to non-image fill). The
non-zero pixel identity values can be referenced to the alphanumeric attribute labels in
the metadata records. The pixel-identity images can be used to disaggregate a composite
image into its constituent source images in order to accommodate scene-specific processing
requirements (e.g., atmospheric correction, normalization of solar illumination angles).
- The following systematic, radiometric, and geometric corrections are applied to 1970's
MSS CCT-X data to generate the EROS Digital Image Processing System's EDIPS-P product. The
CCT-X formatted data are preprocessed to correct for line length adjustments, variable
detector response, band registration, nonlinear mirror-scan velocity, Earth rotational
skew, and detector-to-detector offsets. The images are destriped to compensate for
variations in the radiometric response of the individual detectors prior to geometric
registration, because the noise is scan-line dependent. Using the satellite ephemeris data
and platform navigation model, an interim systematic correction is then applied to
generate a UTM-projected output image with a north-up orientation. Automated
cross-correlation procedures (Bernstein, 1983; Scambos and others, 1992) are then
implemented to extract control points from the 1970's and 1980's images to compute
coefficients for image-to-image registration. This involves the use of a single band from
each of the 1970's input images. Once an accurate transformation is developed, the grid
for the interim systematic correction is convolved with the image-to-image transformation
grid to produce coefficients, which facilitate a single-step registration of the 1970's
P-product with the map-registered 1980's image. The net result is an image registration
procedure that only involves one step of resampling. As of July 28, 1994, a full terrain
correction is also applied to the 1970's image by correcting for the effects of relief
displacement on a pixel-by-pixel basis using the previously created DEM image.
- Cross-correlation procedures are also used to extract over 100 control points that are
used for verification of image-to-image registration quality (1970's to 1980's) with
target total RMSEs of less than 1.0 pixel. Previous studies have shown that the use of
polynomial transformations alone on CCT-X format data yield only a 1.5-pixel to 2.0-pixel
internal image accuracy once map projected, but the use of a satellite model overcomes
this problem. Should the scene fail to meet quality objectives, image-to-image
cross-correlation parameters may be altered and new registration control extracted or
hand-selected image-to-image control may be used.
- The last step involves the creation of a pixel-identity band to accompany each of the
1970's images. Each pixel identity value is indexed to the specific 1970's scene used to
fill-in the WRS-2 path/row tile with pixel values of 0 representing non-image fill.
Typically, two or more 1970's images are required to provide complete coverage of a WRS-2
path/row tile.
- The procedures for the 1990's image registration are similar to those for the 1970's
data except that the 1990's data are acquired as P-level products. An interim systematic
correction is applied to generate a north-up, UTM-projected image. Automated
cross-correlation procedures are used to select control points and a transformation grid
is computed for the image-to-image registration. The interim and precision transformation
grids are convolved into a single grid which is then applied to the 1990's input to create
its 1980's coregistered equivalent. Similar to the 1970's processing, this involves only
one step of resampling. As of July 28, 1994, a full terrain correction is also applied to
the 1990's image by correcting for the effects of relief displacement on a pixel-by-pixel
basis using the previously corrected DEM image.
- The verification of image-to-image registration quality is performed using
cross-correlation procedures as was performed on the 1970's image. The target RMSE for
this registration is less than 1.0 pixel. Should the scene fail to meet quality
objectives, image-to-image cross-correlation parameters may be altered and new
registration control extracted or hand-selected image-to-image control may be used.
- Similar to the 1980's image, the 1990's component of each triplicate is a six-band image
comprised of MSS bands 1 through 4, an NDVI image, and a pixel-identity image.
- Prior to March 20, 1995, cloud-reduced compositing was performed after all the image
data were coregistered. This step was performed only in cases where 1990's scenes with 30
percent or less cloud cover were not available. To minimize the amount of cloud cover in
the 1980's or 1990's triplicate component, the EROS Data Center (EDC) adapted Advanced
Very High Resolution Radiometer (AVHRR) cloud compositing procedures for use in NALC
triplicate generation (Eidenshink, 1992; Holben, 1986). The compositing process operates
on image pairs and is based on the NDVI:
(band 4 - band 2)/(band 4 + band 2)
- This index is sensitive to variations in surface characteristics, such as biomass, and
is sensitive to clouds (Justice and others, 1985). The NDVI is computed for each of the
images to be used for compositing purposes. The maximum NDVI value determines which input
image pixel brightness values will be used to constitute the output image. This maximum
NDVI decision rule is computationally efficient and yields consistent results. A 1980's
triplicate component which has been composited or a 1990's triplicate component which has
been composited, or both components, will have a maximum NDVI image and a pixel-identity
image.
- The NALC triplicate production process has undergone several modifications since
processing began in January 1993:
- January 1993: Triplicate production begins.
- March 15, 1993: Ended the compositing of 1970's images. Multiple 1970's scenes were
mosaicked prior to this date. The 1970's mosaicked images for the 15 triplicates completed
before this date were separated into their individual components.
- March 19, 1993: Ended variable product size. Began standardizing triplicate dimensions
at 5,000-by-5,000 pixels. Prior to this date, product size was determined by adding a set
amount of padding around the registered image data.
- June 10, 1993: Ended standardized 5,000-by-5,000 pixel triplicate dimensions. Back to
variable triplicate size. Began annotating triplicate components with project, scene date,
path/row, and DEM data source.
- July 28, 1994: Full terrain correction implemented on all triplicate components.
- March 20, 1995: Ended the compositing of 1990's scenes.
- 5.0 Restrictions
The Digital Terrain Elevation Data (DTED) for Mexico were acquired from the Instituto
Nacional de Estadistica, Geografia e Informatica (INEGI), and the distribution of these
data is restricted. Only nonprofit organizations may acquire these data upon signing the
restricted distribution form stating that the DEM data will be used for research purposes
only and that the data will not be redistributed to any third parties.
- 6.0 USGS Contact
Customer Services
U.S. Geological Survey
EROS Data Center
47914 252nd Street
Sioux Falls, SD 57198-0001
Tel: 800-252-4547
Tel: 605-594-6151
TDD: 605-594-6933
Fax: 605-594-6589
Email: custserv@usgs.gov
- 7.0 References
Bernstein, Ralph, 1983, Image geometry and rectification, in Colwell, R.N., ed., Manual
of Remote Sensing: Falls Church, Va., American Society of Photogrammetry, p. 881-884.
Eidenshink, J.C., 1992, The 1990 conterminous U.S. AVHRR data set: Photogrammetric
Engineering and Remote Sensing, v. 58, no. 6, p. 809-813.
Holben, B.N., 1986, Characteristics of maximum-value composite images from temporal
AVHRR data: International Journal of Remote Sensing, v. 7, no. 11, p. 1475-1497.
Justice, C.O., Townsend, J.R., Holben, B.N., and Tucker, C.J., 1985, Analysis of the
phenology of global vegetation using meteorological satellite data: International Journal
of Remote Sensing, v. 6, no. 8, p. 1271-1318.
Lunetta, R.S., and Sturdevant, J.A., 1993, The North American Landscape
Characterization Landsat Pathfinder Project, in Pettinger, L.R., ed., Pecora 12 Symposium,
Land Information from Space-Based Systems, Proceedings: Bethesda, Md., American Society of
Photogrammetry and Remote Sensing, p. 363-371.
Scambos, T.A., Dutkiewicz, M.J., Wilson, J.C., and Bindschadler, R.A., 1992,
Application of image cross-correlation to the measurement of glacier velocity using
satellite image data: Remote Sensing of Environment, v. 42, no. 3, p. 177-186.
U.S. Geological Survey, 1987, Digital elevation models, US GeoData Users Guide 5:
Reston, Va., U.S. Geological Survey, 38 p.
U.S. Geological Survey, 1989, Digital line graphs from 1:100,000-scale maps, US GeoData
Users Guide 2: Reston, Va., U.S. Geological Survey, 88 p.
- 8.0 Appendices
- 8.1 Sample Image Metadata
path_nbr |
= |
46 |
row_nbr |
= |
26 |
ctr_latitude |
= |
48.86666 |
ctr_longitude |
= |
-121.31666 |
proc_level |
= |
T |
scene_decade |
= |
80 |
date_entered |
= |
11/01/94 |
map_projection_code |
= |
U |
data_format |
= |
EDIP |
resampling_tech |
= |
C |
scene_id_1 |
= |
5046026008523590 |
cloud_cover_1 |
= |
0 |
control_pts_1 |
= |
44 |
rms_err_1 |
= |
0.86 |
acq_date_1 |
= |
08/28/85 |
sun_elev_1 |
= |
45 |
sun_azimuth_1 |
= |
133 |
restriction_code_dem |
= |
NO |
comments_1 |
= |
None |
- 8.2 Metadata Field Descriptions
- Iterations of fields may apply.
- _n = scene number [_1, _2, _3]
- PATH_NBR = A nominal Landsat satellite track (path) as defined by the Worldwide
Reference System. All NALC data are referenced to WRS-2 (Landsats 4 and 5). Valid values
are: 010-048
- ROW_NBR = A nominal center latitude line of a Landsat image as defined by the Worldwide
Reference System. The row indicator represents scene centers that are chosen at
23.92-second (Landsats 4 and 5) increments along the orbital track in either direction of
the equator. Valid values are: 026-050 = Northern Hemisphere (Descending)
- CTR_LATITUDE = Center latitude of triplicate WRS-2 path/row. The plus (+) sign indicates
the coordinate is in the Northern Hemisphere. All coordinates are stored as decimal
degrees.
- CTR_LONGITUDE = Center longitude of triplicate WRS-2 path/row. The minus (-) sign
indicates the coordinate is in the Western Hemisphere. All coordinates are stored as
decimal degrees.
- PROC_LEVEL = Level of processing performed on the scene. Valid values are:
C |
= |
Composite |
E |
= |
DEM extracted |
G |
= |
Geocoded/georegistered |
T |
= |
Terrain corrected/georegistered |
- SCENE_DECADE = The decade of the scene (70, 80, 90, 0=DEM).
- DATE_ENTERED = The date the metadata record was added to the data base.
- MAP_PROJECTION_CODE = Map projection. Valid value is:
U |
= |
Universal Transverse Mercator (UTM) |
- DATA_FORMAT = The data's original input format. Valid values are:
CCTX |
= |
EDC computer compatible tape in X format |
EDIP |
= |
EROS Digital Image Processing System's format |
DEM |
= |
Digital elevation model format |
FAST |
= |
EOSAT's Fast Format |
- RESAMPLING_TECH = Resampling technique used to radiometrically process the data. Valid values are:
BI |
= |
Bilinear |
CC |
= |
Cubic convolution |
- SCENE_ID_n = Identification for a systematically corrected scene. If more than one scene
ID is listed, then each listed scene was used in the generation of a composite.
- CLOUD_COVER_n = Percentage of image obscured by clouds and cloud shadows for the scene.
Represented in increments of 10 percent.
- CONTROL_PTS_n = Number of geographic control points used for the scene.
- RMS_ERR_n = The average root-mean-square error derived using the scene's control points.
- ACQ_DATE_n = The acquisition date applicable to the scene. Current Landsat operating
window: 1972-Present
- SUN_ELEV_n = The elevation angle of the Sun above the horizon in degrees. Valid values
are: 0-90
- SUN_AZIMUTH_n = The azimuth angle of the Sun measured clockwise from north in degrees.
Valid values are: 0-360
- RESTRICTION_CODE_DEM = A data usage restriction applied to data outside the United
States. Valid values are:
NO |
= |
A usage restriction does not exist on these data. |
YES |
= |
INEGI DEM data for Mexico. Usage restriction. |
- COMMENTS_n = Field for comments or problem statements applicable to the scene.
- 8.3 Sample Data Descriptor
- Information in the data descriptor file that is of direct interest to users
- (PARAMETER:VALUE) includes:
- NL:Number of Lines
- NS:Number of Samples
- NB:Number of Bands
- PROJ.CODE:Map Projection Code (always UTM)
- ZONE CODE:UTM Zone
- ULcorner:UTM northing, easting of upper left corner
- URcorner:UTM northing, easting of upper right corner
- LLcorner:UTM northing, easting of lower left corner
- LRcorner:UTM northing, easting of lower right corner
- PROJ.UNITS:Projection Units (meters)
- The four corners defined by ULcorner, URcorner, LLcorner, LRcorner are the UTM
coordinates for the corners of the data file, including the zero-fill area. The
coordinates for the actual corners of the image must be calculated as offsets from the
file corners by multiplying the number of line and sample offsets by 60, because the pixel
dimensions are 60 meters by 60 meters.
- The Projection Parameters (PROJ. PARM) and MINIMUM/MAXIMUM band values are not valid.
The DATA SOURCE, capture direction (CAPT. DIRECTION), DATE (excluding the date last
modified), and TIME fields correspond to the 1980's reference image. Projection
information and corner coordinates are always the same for each component of a triplicate.
All other parameters and values relate to EDC's processing software and are not relevant
to NALC customers.
- Starting July 28, 1994, full terrain correction was implemented on all triplicate
components. The image naming convention was changed at the same time. Samples of the two
naming conventions follow:
- Image Naming Convention (pre-July 28, 1994): 85068515574x0.trimp
- Image Naming Convention (post-July 28, 1994): p030r033_80_trimp
- IMAGE NAME:85068515574x0.trimp
- DTYPE:BYTE
LAST MODIFIED: |
DATE:10-Feb-93 |
TIME:1643:01 |
- SYSTEM:ieee-std
- PROJ. CODE:(1)UTM
- Valid:VALID
- ZONE CODE:15
- Valid:VALID
- DATUM CODE:0
- Valid:VALID
- PROJ. PARM:
- Valid:INVALID
- A: 0.000000000000000E+00 0.00000000000000E-00
- 0.00000000000000E-00
- B: 0.00000000000000E+00 0.00000000000000E+00
- 0.00000000000000E+00
- C: 0.00000000000000E+00 0.00000000000000E+00
- 0.00000000000000E+00
- D: 0.00000000000000E+00 0.00000000000000E+00
- 0.00000000000000E+00
- E: 0.00000000000000E+00 0.00000000000000E+00
- 0.00000000000000E+00
- CORNER COOR:
- Valid:VALID
- ULcorner: 1.70538000000000E+06 4.44960000000000E+05
- URcorner: 1.70538000000000E+06 7.44900000000000E+05
- LLcorner: 1.40544000000000E+06 4.44960000000000E+05
- LRcorner: 1.40544000000000E+06 7.44900000000000E+05
- PROJ. DIST: 6.00000000000000E+01 6.00000000000000E+01
- Valid:VALID
- PROJ. UNITS:METERS
- Valid:VALID
- INCREMENT:1.00000000000000E+00 1.00000000000000E+00
- Valid:VALID
- MASTER COOR:1 1
- IMAGE NAME:85068515574x0.trimp
- BAND NO:1
- MINIMUM:0.00000000000000E+00
- Valid:INVALID
- MAXIMUM:0.00000000000000E+00
- Valid:INVALID
- DATA SOURCE:landsat 5
- SENSOR TYPE:mss
- CAPT. DIRECTION:descending
- DATE:15-JAN-86
- TIME:1557:4
- IMAGE NAME:85068515574x0.trimp
- BAND NO:2
- MINIMUM:0.00000000000000E+00
- Valid:INVALID
- MAXIMUM:0.00000000000000E+00
- Valid:INVALID
- DATA SOURCE:landsat 5
- SENSOR TYPE:mss
- CAPT. DIRECTION:descending
- DATE:15-JAN-86
- TIME:1557:4
- IMAGE NAME:85068515574x0.trimp
- BAND NO:3
- MINIMUM:0.00000000000000E+00
- Valid:INVALID
- MAXIMUM:0.00000000000000E+00
- Valid:INVALID
- DATA SOURCE:landsat 5
- SENSOR TYPE:mss
- CAPT. DIRECTION:descending
- DATE:15-JAN-86
- TIME:1557:4
- IMAGE NAME:85068515574x0.trimp
- BAND NO:4
- MINIMUM:0.00000000000000E+00
- Valid:INVALID
- MAXIMUM:0.00000000000000E+00
- Valid:INVALID
- DATA SOURCE:landsat 5
- SENSOR TYPE:mss
- CAPT. DIRECTION:descending
- DATE:15-JAN-86
- TIME:1557:4
- 8.4 NALC Tape Mapper File Order and File Descriptions
- Information in this appendix, and in all following appendices, is based upon a standard
NALC triplicate, which contains one DEM, two 1970's images, one 1980's image, and one
1990's image. The actual number of files may vary slightly, depending upon the NALC
triplicate.
- Each image file is in band-sequential (BSQ) format and has corresponding files in ASCII
format, including a data descriptor file and a metadata file. If a waiver is not signed
for triplicates that contain restricted DEM data for Mexico, then the NALC README file is
directly followed by files for an MSS 1970's scene.
- File 1. NALC README
- File 2. DEM Data Descriptor File
- File 3. DEM Image Data File
- File 4. DEM Metadata File
- File 5. First 1970's Scene, Data Descriptor File
- File 6. First 1970's Scene, Image Data File
- File 7. First 1970's Scene, Metadata File
- File 8. Second 1970's Scene, Data Descriptor File
- File 9. Second 1970's Scene, Image Data File
- File 10. Second 1970's Scene, Metadata File
- File 11. 1980's Scene, Data Descriptor File
- File 12. 1980's Scene, Image Data File
- File 13. 1980's Scene, Metadata File
- File 14. 1990's Scene, Data Descriptor File
- File 15. 1990's Scene, Image Data File
- File 16. 1990's Scene, Metadata File
- The content of the NALC README file is self explanatory, while descriptions of the
remaining files follow:
- Data Descriptor File: Contains ASCII dump of data descriptor record.
- Image Data File: Either contains a single band of DEM image data or contains MSS image
data in a band-sequential format.
- Metadata File: Either contains DEM image metadata or contains MSS image metadata.
- The image files vary in size (i.e., number of bands, number of lines, and number of
samples), depending on the requirements for cloud compositing and depending on the
creation date of the triplicate. As of June 14, 1993, all 1970's images contain five bands
(i.e., MSS bands 1 through 4 and a pixel-identity image) and all 1980's and 1990's images
contain six bands (i.e., MSS bands 1 through 4, an NDVI image, and a pixel-identity
image).
- Users are encouraged to first examine the data descriptor file, because it specifies the
number of lines (NL), the number of samples (NS), and the number of bands (NB) in the
image, as well as specifying geographic coordinates. The UTM corner points correspond to
the four corners of the array and are always based on the 1980's scene (also referred to
as the reference scene). The array contains the fully geocoded scene including the
zero-fill and annotation areas.
- The DEM files and the image files contain the same NL and NS dimensions. The DEM is in a
16-bit INTEGER*2 data format (also known as a 16-bit signed integer format), whereas the
MSS images are BYTE data (also known as 8-bit unsigned integer data).
- The number of bytes per record in image files is equivalent to the number of pixels per
line. The total number of records per file, divided by the number of bands, is equivalent
to the total number of lines in the image.
- Files are written to tape in chronological order by date and preceded by DEM files where
applicable (i.e., DEM file(s); 1970's file(s); 1980's file(s); and 1990's file(s)). If a
waiver is not signed for triplicates that contain restricted DEM data for Mexico, then
only the MSS portion of the triplicate is provided (i.e., 1970's file(s); 1980's file(s);
and 1990's file(s)).
- 8.5 Sample NALC Tape Mapper
- The following represents a typical mapper for a NALC tape that contains a NALC README
file, a DEM, two 1970's images, a 1980's image, a 1990's image, and their associated data
descriptor and metadata files. The DEM image file consists of INTEGER*2 data (16-bit
signed integer data) so the total number of bytes per record is twice the number of
samples per line. The total number of records in the DEM image file is equivalent to the
total number of lines in the image. If a waiver is not signed for triplicates that contain
restricted DEM data for Mexico, then the tape will contain the NALC README file followed
by the data descriptor file for the first 1970's image.
- The 1970's, 1980's, and 1990's MSS images are BYTE data (8-bit unsigned integer data).
Therefore, the number of bytes per record is equivalent to the number of samples per line
in the image. The 1970's images contain five bands (MSS bands 1 through 4 and a
pixel-identity image); thus, the total number of records in the image file equals five
times the number of lines in the image. The 1980's and 1990's images contain six bands
each (MSS bands 1 through 4, an NDVI image, and a pixel-identity image). Consequently,
each of these files has a total number of records that is equivalent to six times the
number of lines in the image.
- We recommend that users read the NALC README and data descriptor files first. These
files describe the characteristics of the data sets, which are typically transcribed to
the proper parameters for retrieving the image data from tape.
- ********** Mapper of tape [n] mounted on DRIVE [n] **********
- 6 RECORDS 4097 BYTES LONG
- 1 RECORDS 1784 BYTES LONG
- END OF FILE #1 >>>>> 7 TOTAL RECORDS. -- NALC README
- 1 RECORDS 1919 BYTES LONG
- END OF FILE #2 >>>>> 1 TOTAL RECORDS. -- DEM Data Descriptor
- 3883 RECORDS 8194 BYTES LONG
- END OF FILE #3 >>>>> 3883 TOTAL RECORDS. -- DEM Image
- 1 RECORDS 674 BYTES LONG
- END OF FILE #4 >>>>> 1 TOTAL RECORDS. -- DEM Metadata
- 1 RECORDS 4097 BYTES LONG
- 1 RECORDS 157 BYTES LONG
- END OF FILE #5 >>>>> 2 TOTAL RECORDS. -- 1st 1970's MSS Image
Data Descriptor
- 19415 RECORDS 4097 BYTES LONG
- END OF FILE #6 >>>>> 19415 TOTAL RECORDS. -- 1st 1970's MSS Image
- 1 RECORDS 674 BYTES LONG
- END OF FILE #7 >>>>> 1 TOTAL RECORDS. -- 1st 1970's MSS Image Metadata
- 1 RECORDS 3786 BYTES LONG
- END OF FILE #8 >>>>> 1 TOTAL RECORDS. -- 2nd 1970's MSS Image
Data Descriptor
- 19415 RECORDS 4097 BYTES LONG
- END OF FILE #9 >>>>> 19415 TOTAL RECORDS. -- 2nd 1970's MSS Image
- 1 RECORDS 674 BYTES LONG
- END OF FILE #10 >>>>> 1 TOTAL RECORDS. -- 2nd 1970's MSS Image Metadata
- 1 RECORDS 3786 BYTES LONG
- END OF FILE #11 >>>>> 1 TOTAL RECORDS. -- 1980's MSS Image
Data Descriptor
- 23298 RECORDS 4097 BYTES LONG
- END OF FILE #12 >>>>> 23298 TOTAL RECORDS. -- 1980's MSS Image
- 1 RECORDS 686 BYTES LONG
- END OF FILE #13 >>>>> 1 TOTAL RECORDS. -- 1980's MSS Image Metadata
- 1 RECORDS 3786 BYTES LONG
- END OF FILE #14 >>>>> 1 TOTAL RECORDS. -- 1990's MSS Image
Data Descriptor
- 23298 RECORDS 4097 BYTES LONG
- END OF FILE #15 >>>>> 23298 TOTAL RECORDS. -- 1990's MSS Image
- 1 RECORDS 686 BYTES LONG
- END OF FILE #16 >>>>> 1 TOTAL RECORDS. -- 1990's MSS Image Metadata
- ********** END OF VOLUME **********
- --------------------------------
- 89327 RECORDS IN VOLUME.
- 8.6 Retrieving Tape Files Using Unix "DD"
- The following example illustrates how the files can be read from tape using the Unix
"dd" utility. The example uses information contained in the preceding sample
tape mapper. Substitute the appropriate values for your path/row. When using
"dd" to retrieve files from a tape, always use the number of bytes in the mapper
for your input block size (ibs) in the "dd" command.
- To retrieve the NALC README file:
- dd if=(device name) of=(output file name) ibs=4097
- To retrieve the DEM data descriptor file:
- dd if=(device name) of=(output file name) ibs=1919
- To retrieve the DEM image file:
- dd if=(device name) of=(output file name) ibs=8194
- There are 8194 bytes in the tape mapper for the DEM image, which is twice the number of
bytes that are found in the MSS images. This is because DEM data are stored in INTEGER*2
(16-bit signed integer) format and requires two bytes per pixel. The number of records in
the DEM file is exactly equal to the number of lines in the image (no division by number
of bands is necessary to find the number of lines, since the DEM is a one-band image).
- To retrieve the DEM metadata file:
- dd if=(device name) of=(output file name) ibs=674
- The tape should now be at the data descriptor file for the first 1970's MSS image.
Repeat the previous steps for each set of files, using the appropriate input block size
(ibs) each time.
- When the tape is positioned at the first 1970's MSS image file, it is then possible to:
(1) load the image one band at a time with five separate output files (i.e., multiple
single-band files) or (2) load all bands into one file (one multiple-band file in BSQ
format).
- To load all five bands into one BSQ file, use the following "dd" command:
- dd if=(device name) of=(output image name) ibs=4097
- To load each band into its own separate file, use the following "dd" command:
- dd if=(device name) of=(output image name) ibs=4097 count=3883
- The additional COUNT parameter is required when loading each band into a separate file.
The value for COUNT is equal to the number of lines in the image. Again, the number of
lines in the image is found by dividing the number of records by the number of bands. All
MSS data are stored as BYTE (8-bit unsigned integer) data.
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