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IceBridge CAMBOT L1B Geolocated Images

This data set contains Continuous Airborne Mapping By Optical Translator (CAMBOT) images taken over Antarctica and Greenland. The data were collected as part of Operation IceBridge funded campaigns and are available via FTP for periodic, ongoing campaigns from 31 March 2009 to the present.

Operation IceBridge products may include test flight data that are not useful for research and scientific analysis. Test flights usually occur at the beginning of campaigns. Users should read flight reports for the flights that collected any of the data they intend to use. Check IceBridge campaign Flight Reports for dates and information about test flights.

2. Detailed Data Description

The data set contains original CAMBOT files and full size Joint Pictures Expert Group (JPEG) images, with associated Keyhole Markup Language (KML) files, rotated and reduced-resolution Portable Network Graphics (PNG) image files, and position, altitude and trajectory files.

Format

IceBridge CAMBOT Level-1B Geolocated Images data set files are in JPEG, PNG, KML, and ASCII fixed-field format.

File and Directory Structure

Data files are organized on the FTP site, ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE_FTP/, as described in Figure 1.

Figure 1. Directory Structure

In each directory, data are organized into sub-directories named by mission date /YYYY_MM_DD/, such as /2010_03_23/, where: YYYY is the mission year, MM is the month, and DD is the day.

Each /YYYY_MM_DD/ directory contains CAMBOT .cam files, and additional sub-diretories described below.

/YYYYMMDD/ (example /2010032) contains KML files, script and utility files, and subdirectories /exif/ and /rotd/ described below.

/YYYYMMDD_HHMM/ (example: /20100323_1507/) contains un-rotated full-sized CAMBOT JPEG images. HHMM (1507 in this example) is the hour and minute timestamp, 15:07, when the folder was created and when the CAMBOT recording session was started.

/exif/ contains text files of Exchangeable Image File (EXIF) information.

/rotd/ contains rotated reduced-resolution CAMBOT images in PNG files.

File Naming Convention

CAMBOT Files

CAMBOT geolocation files (.cam) with position and altitude information are named according to the following convention and as described in Table 1.

20100323_121757.atm4cT3.cam

YYYYMMDD_HHMMSS.atm4cT3.cam

Where:

Table 1. Geolocation File Naming Convention

Variable	Description
YYYY	four-digit year
MM	two-digit month
DD	two-digit day
HH	hour of image capture
MM	minute of image capture
SS	second of image capture
atm4c	Airborne Topographic Mapper instrument identification (ATM)
T3	T3 = ATM 23-degree off-nadir scan angle
.cam	indicates CAMBOT geolocation file

The CAMBOT files correlate one-to-one with the Qfit (*.qi) files in the IceBridge ATM L1B Qfit Elevation and Return Strength data set.

Note: Some .cam files from the 2009 Greenland and 2009 Antarctica campaigns include "rangeExample" in the file name. This is an outdated filename descriptor, and is not used in later campaigns.

Image Files

Image files and associated text files are named according to the following convention and as described in Table 2.

IMG_00308.JPG
IMG_00308.png
IMG_00308.txt

IMG_00308.NNN

Where:

Table 2. Image File Naming Convention

Variable	Description
IMG	indicates image
nnnnn	image number
.NNN	indicates image file type (.JPG or .png); or text file (.txt)

KML Files

KML files are named according to the following convention and as described in Table 3.

cambot_1_20101016.kml

cambot_n_YYYYMMDD.kml

Where:

Table 3. KML File Naming Convention

Variable	Description
cambot	refers to CAMBOT instrument
n	version of CAMBOT processing
YYYY	four-digit year
MM	two-digit month
DD	two-digit day
.kml	indicates kml file type

Note: Some KML files from the 2009 Greenland, 2009 Antarctica, and 2010 Greenland campaigns include .kml1, kml2, or kml3 in the file name. These files were intermediate steps in the creation of the final kml, and are not used in campaigns after 2010 Greenland. The descriptors indicate: kml = google earth logo, kml1= google earth placemark file, kml2 = google earth ground overlay file, kml3 = google earth flight tracks file.

Applanix Trajectory Files

Applanix trajectory files are named according to the following convention and as described in Table 4.

BD960_16Mar11_PPPK.out

BD960_DDMmmYY_PPPK.out

Where:

Table 4. KML File Naming Convention

Variable	Description
BD960	internal GPS receiver designation
DD	2-digit day
Mmm	3-letter month
YY	2-digit year
PPP	indicates Precise Point Positioning processing method
K	designation for creator of the trajectory
.out	indicates trajectory output file

During the 2009 Greenland, 2009 Antarctica, and 2010 Greenland campaigns, trajectory files were ATM trajectories derived from GPS measurements. After the 2010 Greenland campaign, these files are no longer used or included with the CAMBOT data. The file names are described below and in Table 5.

091016_aa_l12_cfm_itrf05_23mar10_palm_amu2
091103_aa_l12_cfm_itrf05_18may10_palm_roth
090331_aa_l12_cfm_itrf05_12aug_898b

YYMMDD_aa_l12_cfm_itrf05_ddmmmyy_nnnn_nnnn

Where:

Table 5. ATM / GPS Trajectory File Naming Convention (2009 Greenland, 2009 Antarctica, and 2010 Greenland only)

Variable	Description
YY	2-digit year
MM	2-digit month
DD	2-digit day
aa	internal antenna reference identification
l12	indicates that trajectory uses information from both L1C and L2C GPS signals
cfm	initials of trajectory creator
itrf05	reference frame used for the trajectory
dd	2-digit day of trajectory creation date
mmm	three-character name of month of trajectory creation date
yy	2-digit year of trajectory creation date
nnnn_mmmm	4-letter designations for GPS base stations used in the processing (examples palm, amu2, 898b)

Additional Files

Additional files included in this data set are described in Table 6.

Table 6. Additional File Names and Descriptions

Variable	Description
cambot.log	The CAMBOT acquisition software creates a cambot.log file which timestamps each command and response from the camera. The cambot.log file allows for sub-second timing of each image in an attempt to better position each image along the flight track.
gps.txt	Intermidiate processing file; contains image filename, a corrected timestamp (GPS time), position data, and attitude data.
gps.err	GPS error file. Used during the 2009 Greenland, 2009 Antarctica, and 2010 Greenland campaigns, this is an outdated file type and starting with 2010 Antarctica is no longer included with dataset.
picture.txt	Contains the time when each image was taken. A simplified version of the cambot.log file, with the image filename and an ISO-format timestamp.
exif.sh	Script to extract EXIF header information from each image.
rotate.sh	Script to rotate each JPG image to the proper heading, reduce resolution, and save as a transparent PNG.

File Size

CAMBOT (.cam) files range from approximately 62 KB to 400 KB.

ASCII text (.txt) files are approximately 2 KB each.

JPEG files range from approximately 816 KB to 5 MB.

PNG files range from approximately 133 KB to 500 KB.

KML files range from approximately 124 KB to 16 MB.

Volume

Total volume of the data set is approximately 3.3 TB.

Spatial Coverage

Spatial coverage for the IceBridge CAMBOT campaigns includes Greenland and Antarctica. In effect, this represents the coverage noted below.

Greenland:
Southernmost Latitude: 60° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E

Antarctica:
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E

Spatial Resolution

The image files are 3888 pixels width by 2592 pixels height for 2010 and 2011 campaigns, and 2816 pixels width by 1880 pixels height for 2009 campaigns. At 450 m above the ground, each pixel represents 13 cm by 13 cm on the ground. The image footprint at 450 m instrument altitude is 500 m alongtrack by 300 m across track.

Projection and Grid Description

No projection. Data are georeferenced as a series of camera locations: latitude, longitude, elevation and altitude above ground (WGS 84 Datum) and aircraft orientation roll, pitch, and heading.

Temporal Coverage

These data were collected as part of Operation IceBridge funded campaigns from 31 March 2009 to the present.

On 09 April 2011 and 04 May 2011 the aircraft flew calibration flights. No ATM LIDAR science data are provided for these two days in the IceBridge ATM L1B Qfit Elevation and Return Strength data set, but CAMBOT images were captured for both days and are included in this data set.

During the IceBridge 2011 Greenland campaign, the CAMBOT instrument had a shutter failure on 10 May 2011, so there are no CAMBOT data files for the remaining four flights after that date.

Temporal Resolution

IceBridge campaigns are conducted on an annual repeating basis. Arctic and Greenland campaigns are conducted during March, April, and May, and Antarctic campaigns are conducted during October and November.

CAMBOT operates in two modes, sequential and parallel. In sequential mode, one camera is operated at a time, giving a continuous rate of one image every ten seconds. After the compact flash card in the camera fills, the system switches to the next camera while the previous camera is transferring the images to the computer. In parallel mode, both cameras are used simultaneously, giving a rate of one image every five seconds. In parallel mode no images are taken while both cameras transfer images to the computer. The transfer process takes several minutes.

Parameter or Variable

The CAMBOT L1B Geolocated Images data set includes visible imagery, and WGS 84 elevation of ground topography. Also included are .cam files containing aircraft position, altitude, and attitude information, and .kml files that tie the images files together for displaying with Google Earth.

Parameter Description

The CAMBOT (.cam) files are in ASCII fixed-field format. Parameters are described in Table 7.

Table 7. CAMBOT File Parameters and Units

Column	Description	Units
1	GPS time of day	Seconds
2	Latitude	Degrees
3	East longitude	Degrees
4	Aircraft altitude - position of camera above WGS 84 ellipsoid	Meters
5	Altitude of aircraft above ground	Meters
6	Surface height - WGS 84 elevation of ground topography measured by laser	Meters
7	Pitch of aircraft	Degrees
8	Roll of aircraft	Degrees
9	Heading of aircraft	Degrees

Sample Data Record

Below is an excerpt from file 20110316_124420.ATM4BT4.cam. The fields in each record correspond to the columns described in Table 7.

The image below is an excerpt from the 14 April 2010 Greenland image file IMG_03539.JPG.

3. Data Access and Tools

Data Access

Data are available via FTP.

Software and Tools

The image files may be opened by any image display program capable of reading JPEG and PNG files. The KML files may be used with GIS software and earth browsers such as Google Earth, Google Maps. The ASCII fixed-field files may be opened by any text editor or word processing program that reads ASCII text files.

4. Data Acquisition and Processing

Theory of Measurements

CAMBOT is a digital image acquisition system that supports analysis of laser altimeter data from the ATM. The image provides a qualitative high-resolution assessment of the surface structure and lower atmosphere conditions sensed by the ATM. As a passive instrument, using sunlight is the source of illumination, CAMBOT has some limitation, such as shadows, daytime-only operation, and reduced data value under high-cloud or low mist conditions. However, the images are a very high-resolution record of ice structures, nunataks, snow, crevasses, sastrugi, leads and sea ice type.

Data Acquisition Methods

The CAMBOT system takes down-looking images from an aircraft, which are logged directly to a Mac mini data computer. When the acquisition software is started on the data computer, it verifies that an appropriate camera is powered up and connected via USB. Then, the acquisition software sends a set of default camera settings to the camera for initialization. At this point, the system operates in standby mode until the operator clicks on the Start button to begin acquisition. When the Start button is pressed, a directory is made for the current day (of the form YYYYMMDD) in the home directory. Next, a subdirectory is created for this specific CAMBOT recording session (of the form YYYYMMDD_HHNN). Finally, the software sends a trigger to the camera to capture an image. Once captured, the image is immediately transferred back to the data computer and stored in the session subdirectory. The acquisition software sends the image capture signal every four seconds by default, which can be modified in the software settings. During the acquisition, a log file is generated which records a local timestamp based on computer time for the following events:

• Timestamp when capture signal is sent to camera
• Timestamp when image transfer to computer begins
• Timestamp when image transfer to computer ends

Derivation Techniques and Algorithms

The CAMBOT files are created during processing of the ATM laser data and are useful for interpreting the nadir-viewing LIDAR. There is little to no image processing or image data manipulation applied outside of what the Canon Rebel XTi camera does during acquisition of an image and conversion to the JPEG and PNG distribution formats.

Processing Steps

The following processing steps are performed by the data provider for each flight.

1. Assemble the Applanix trajectory and .cam files for the flight into the corresponding CAMBOT data directory. Prepare the .cam files by concatenating all the .cam files into a single file and filtering the resulting files to remove outliers.
2. Create a picture.txt file to assign each raw CAMBOT JPG with a relative timestamp determined by the data computer which recorded the images, which is extracted from the cambot.log file created during acquisition.
3. Correct the relative UTC timestamps to corrected timestamps in the GPS time standard. This is accomplished by applying a single offset to all of the image timestamps in a single flight. This offset is nominally the offset between UTC and GPS time, but can drift day-to-day if the local data computer time is not synchronized to UTC each day.
4. Interpolate the attitude pitch, roll, and heading information from the Applanix trajectory to match the timestamps of the CAMBOT images. Interpolate the positional information (latitude, longitude, altitude, altitude-above-ground) from the filtered .cam file. Create a gps.txt file which contains the image filename, GPS timestamp, aircraft positional information including latitude, longitude, ellipsoid altitude, altitude-above-ground, and attitude information including roll, pitch, heading.
5. Calculate the rotation of the image relative to true north using the heading information of the aircraft, rotate the image, and save a reduced-resolution copy of the resulting image as a transparent PNG.
6. Create a Google Earth KML file to overlay the rotated reduced-resolution images with the proper location and size onto the Google Earth model.

Error Sources

During the IceBridge 2011 Greenland campaign, the CAMBOT instrument had a shutter failure on 10 May 2011, so there are no CAMBOT data files for the remaining four flights after that date.

During the 2012 Greenland campaign, the CAMBOT camera failed shortly before Barrow on 14 March 2012. There was no spare on board due to weight constraints. The backup CAMBOT system was installed prior to the 21 March 2012 flight. Thus, for 15 through 19 March 2012, the data set contains .cam files only; JPG, PNG, and KML files are not included.

Sensor or Instrument Description

The CAMBOT system is comprised of a Canon Rebel XTi (or alternatively the XSi model) camera and a Mac mini running custom data acquisition software. The camera is powered with an AC power adapter and connected to the Mac mini via USB. The camera is outfitted with a Canon Zoom Lens EF-S 18-55 mm lens.

5. References and Related Publications

Related Data Collections

Related Web Sites

6. Document Information

Acronyms and Abbreviations

The acronyms used in this document are listed in Table 8.

Document Creation Date

25 January 2012

Document Revision Date

08 June 2012
02 October 2012
28 November 2012

Document URL

http://nsidc.org/data/docs/daac/icebridge/iocam1b/index.html