MSS Detector Pattern Example (8.3 kb)
The first satellite in the Earth Resources Technology Satellite (ERTS) program was launched July 23, 1972 and designated ERTS 1. In 1975 the program was re-designated as the Landsat program to emphasize its primary area of interest, land resources. The mission of Landsat is to provide for repetitive acquisition of high resolution multispectral data of the earth's surface on a global basis.
The complete Landsat system consisted of an observation platform in a near-polar Earth orbit and ground installations to receive, process, and distribute the data provided by the sensors carried on board the satellite. The platform carried two remote sensor systems, communication links, attitude-control and orbit-adjust systems, and a power supply to send the image to ground receiving stations and to receive ground control commands.
The Landsat satellites are in a sun-synchronous, near polar orbit with a ground swath extending 185 km (115 miles) in both directions. Landsats 1-3 were inclined 99 degrees with an orbital cycle of 18 days and an equatorial crossing of between 8:50 and 9:30 AM local time. Landsat 4 and 5 are inclined 98 degrees, have an orbital cycle of 16 days, and an equatorial crossing of 9:45 AM local time. The altitude of the satellites varied between 920 km (571 miles) for Landsats 1-3 and 705 km (437 miles) for Landsats 4 and 5.
The Landsat Ground Station Operations Working Group (LGSOWG) MSS data base lists all MSS Landsat scenes held by participating countries (excluding USA).
The Landsat system provides for global data between 82 degrees North latitude and 82 degrees South latitude.
The Landsat platforms operate from a sun-synchronous, near polar orbit imaging the same 185 km (115 miles) ground swath every 16 days (formerly 18 days on Landsats 1-3). Multispectral Scanner (MSS) are received directly from Landsats 4 and 5 by the LGSOWG network of worldwide ground stations.
The processing subsystem at each LGSOWG station may vary, but usually consists of a slave and master CPU, an inter-CPU data bus, array processors, and system disks. The slave CPU ingests the data and, together with the array processors, applies the geometric correction transformation. Image enhancement is accomplished by the master CPU through interaction of several devices including the image disk, an array processor (edge enhancement only), and the table-lookup controller. Frame rasterization, field formatting and image data transfer to film and tape recorders is also performed by the master CPU. Control overall process functions is maintained by the master CPU.
An MSS scene has an Instantaneous Field Of View (IFOV) of 68 meters in the cross-track direction by 83 meters in the along-track direction (223.0 by 272.3 feet respectively). To understand this concept consider a ground scene composed of a single 83 by 83 meter area. The scan monitor sensor ensures that the cross-track optical scan is 185 km at nominal altitude regardless of mirror scan nonlinearity or other perturbations of mirror velocity. Cross-track image velocity is nominally 6.82 meters per microsecond. After 9.958 microseconds, the 83 by 83 meter image has moved 67.9 meters. The sample taken at this instant represents 15 meters of previous information and 68 meters of new information.
Therefore, the effective IFOV of the MSS detector in the cross-track direction is considered to be 68 meters which corresponds to a nominal picture element (pixel) ground area of 68 by 83 meters at the satellite nadir point. Using the effective IFOV in area calculation eliminates the overlap in area between adjacent pixels.
Landsats 1-3 provided Earth coverage similar to Landsats 4 and 5. However, the higher altitude of Landsats 1-3 resulted in a different swathing pattern with the IFOV being 56 meters in the cross-track direction by 79 in the along-track direction (183.7 feet by 259.2 feet respectively).
MSS Detector Pattern Example (8.3 kb)
Launch Date Deactivated Sensor
Landsat 1 07/23/72 01/06/78 MSS
Landsat 2 01/22/75 02/25/82 MSS
Landsat 3 03/05/78 03/31/83 MSS
Landsat 4 07/16/82 ---- MSS
Landsat 5 03/01/84 ---- MSS
The Multispectral Scanner (MSS) sensors are line scanning devices observing the earth perpendicular to the orbital track. The cross-track scanning is accomplished by an oscillating mirror; six lines are scanned simultaneously in each of the four spectral bands for each mirror sweep. The forward motion of the satellite provides the along-track scan line progression. All five Landsats have carried the MSS sensor which responds to earth reflected sunlight in four spectral bands. Landsat 3 carried an MSS sensor with an additional band, designated band 8, that responded to thermal (heat) infrared radiation.
Multispectral Scanner (MSS)
Landsats Landsats
1 - 3 4 & 5
Band Band Micrometers Resolution
4 1 .5 - 0.6 80m
5 2 .6 - 0.7 80m
6 3 .7 - 0.8 80m
7 4 .8 - 1.1 80m
8 10.41 - 12.6 237m
Micrometers and their relationship to the electromagnetic spectrum are explained in the glossary.
Two types of image data are offered:
Processing Codes
Fully Processed Partially Processed
MSS = CCT-P MSS = CCT-A
Both processing levels offer either a Band-Interleaved-by-Line (BIL) or a Band-Sequential (BSQ) image data format.
Unlike previous Landsat CCT formats (Landsats 1-3), current CCT's will include a comprehensive field location and data description information superstructure. This superstructure consists of:
The entire superstructure is composed of four records. Three records (volume descriptor, text, file pointer) reside in a volume directory file. The fourth record is the file descriptor record which is the first record of each data file. The four superstructure records are similar to one another in content as well as in format. The purpose of these records is to identify, describe and locate data in the data files. Thus, superstructure records primarily supply information about the data on the CCT rather than carrying data themselves.
To obtain additional LGSOWG MSS information regarding other technical details, ancillary products, and pricing schedules, contact one of the:LGSOWG Stations
The specific LGSOWG station can be determined from the first two characters of each scene's Entity ID based upon:
Online requests for these data can be placed via the U. S. Geological Survey Global Land Information System (GLIS) interactive query system. The GLIS system contains metadata and online samples of Earth science data. With GLIS, you may review metadata, determine product availability, and place online requests for products.
Requests for LGSOWG MSS data will be forwarded to the proper LGSOWG center. U.S. Federal users interested in purchasing data may contact: Customer Services, EROS Data Center
Applications and Related Data Sets
Landsat data are used for many varying studies, inventories and analysis. Crop acreage inventories, timber class identifications, soil identification and mapping, range cover and forage production analysis, plant stress detection, regional land use classifications, generation of photo-maps, mineral and petroleum exploration, pollution monitoring, geological mapping and interpretation, areal snow extent assessments, and shallow bathymetric measurements are but a few of the applications of Landsat MSS data.
Non-image data fields are byte multiple in length. Alphanumeric data fields are ASCII coded and left-justified. Numeric data fields are ASCII coded and right-justified. All binary fields are uncoded, unsigned integer binary numbers. Many header and ancillary data records are represented in one of four special fixed or floating-point formats: fixed-point binary, double precision floating-point binary, single precision floating-point binary and fixed-point binary grid value. Image data is right-justified in a byte with the most significant bit zero-filled. A data range from 0 to 127 is allowed with zero as low radiance.
On Landsat CCT's, a physical record is equivalent to a logical record. Volume descriptor, file pointer, file descriptor, header, ancillary, annotation, image, trailer, and text data are the different types of records. Records are structured to contain a record number, a record type code, the record length in bytes, data and optional zero fill. Records are separated by inter-record gaps (IRG) and records are not split between physical tape volumes.
The record number is a four-byte binary number indicating the sequence of the record within the file. The first record of the file is numbered one with the record number incrementing by one per record.
Bytes five through eight of every record contain four one-byte codes which classify the data content of the record. Bytes nine through twelve record the record length. This is a binary, right-justified number with the left-most bit being the most significant. Volume directory and null volume directory records are 360 bytes in length. All other records on the CCT are 3600 bytes in length.
A file is a collection of physical records preceded and followed by end-of-file (EOF) indicators. All files, minus volume directory files, have a file descriptor record as the first record. This is followed by the data records of the file. All records of a file are of a constant record length. On MSS CCT's there are four types of files:
A logical file is equivalent to a physical file except in the case of image files. An image file (and no other file) may be split between reels of CCT's on record boundaries. In that case logical image files would not equal physical image files. One image file equals either one image (one band) of data when the format is BSQ, or all bands in the BIL format.
The volume directory file is the first file of every logical volume. It is composed of a volume descriptor record, a text record and a series of file pointer records. Every physical volume (a tape) also starts with a volume directory file since the tape is either the start of a logical volume or else a logical volume is contained on the tape, in which case the updated volume directory is recorded at the start of the physical volume. The volume descriptor record identifies the logical volume and the number of files the logical volume contains. A text record follows the volume descriptor record and identifies the type of data contained in the logical volume. There is a file pointer record for each data file of the logical volume, indicating each file's class, format, and attributes.
All logical volumes have a volume directory as the first file. This is followed by leader, image, and trailer data files and is concluded with a null volume directory. When a logical volume is split between physical volumes, the volume directory is repeated at the start of the continuation tape. All logical volumes conclude with a null volume directory (one per logical volume in all cases).
A small piece of reflective tape is located on the non-recording side of a CCT several feet from the beginning of each reel. This beginning-of-tape (BOT) indicates the beginning of the tape for reading and writing. An initial gap of between three inches and 25 feet separates the first record on a CCT from the BOT. An inter-record gap (IRG) of 0.6 inches separates multiple records in a file. The end-of-file (EOF) mark is a specially coded block of data which separates files on a CCT. The end-of-volume (EOV) indicator consists of two consecutive EOF's and marks the end of recorded data on the physical volume.
A small piece of reflective tape is located on the non-recording side of a CCT several feet from the end of each reel. This end-of-tape (EOT) marker indicates the end of the permissible recording area. The end-of-set (EOS) mark consists of three consecutive EOF's and occurs on the last physical volume of a volume set. The pre-superstructure (BIP-2) one band tape layout is below:
Beginning in the spring of 1979, the MSS sensor aboard Landsat 3 began to experience a problem with proper synchronization of scan lines. NASA performed a series of tests during the period of April 8-24, 1979, in an attempt to correct the situation. However, in the fall of 1979 the problem began occurring with increasing frequency. After that period line-start anomalies affected 20% to 40% of all Landsat 3 MSS images acquired.
The MSS sensor is equipped with a hardware feature that generates a line-start pulse to activate the MSS detectors at the beginning of each mirror sweep. The problem occurs when this start pulse is either absent or of abnormally low amplitude. Because the detectors are not activated at the appropriate time, no data are acquired during the initial part of the scan. A second pulse does activate the detectors when the mirror is about 30% of the way across a scan, but the early (western) portion of the intended scan area is lost by this time.
Because there are six detectors per band, multiples of the six scan lines are involved. The number of scan lines affected in a given frame is random and depends on how many line-start pulses are missed. As many as 40% of the scenes are affected, and the number of affected scans varies from 10% to 90% of the scans in the image.
Before the occurrence of this problem, all scan lines were left-justified during routine processing at NASA; that is, they were aligned at the left side of the image. For every line-start pulse missed, a set of six scan lines was thus aligned with those that had normal start pulses. This caused that set of scan lines to shift on the ground about 48 km (29.8 miles) to the left of where they should have been.
After the first appearance of the line-start anomaly, NASA contracted to have the ground hardware modified to alleviate this problem. Basically, the hardware properly aligns the good portions of the affected scan lines with respect to the other scan lines so that the ground features line up correctly. Unfortunately, the 30% of the data that was missed in each scan line is lost; missing areas are represented in the image as blanks. The corrected images are technically more than 70% usable, meaning that much of the image area is unaffected, but their appearance is hardly aesthetic. All quality code references to line-start anomaly scenes refer only to the unaffected areas. --------------755A2E7D7380--