Mercator - Of, relating to, or drawn on the Mercator projection (a conformal map projection with the meridians drawn parallel to each other and the parallels of latitude drawn as straight lines whose distance from each other increases with their distance from the equator).

Metadata - A set of descriptive information about the scene data contained in the archive. The information is sufficient for a user, during the process of scene query and selection, to determine at a minimum geographic coverage, date of collection sensor gain mode, time of acquisition, cloud cover, and other quality measurements.

Missions Operations Center (MOC) - The place where the satellite or spacecraft receives coded instructions and delivers data. The coordination place (usually on Earth) for any space mission.

Modulation - The variation of a property of an electromagnetic wave or signal, such as its amplitude, frequency, or phase.

Mosaicking: - The assembling of photographs or other images whose edges are cut and matched to form a continuous photographic representation of a portion of the Earth's surface.

Multispectral - Sensing in usually 4 distinct wavelength bands (equivalent to colors, not all of which are visible to the human eye).  Because the data handling capacity of the sensor is spread over these different wavelengths, this usually translates to lower resolution than panchromatic. 

Multispectral image - A remote sensing image created using data collected from more than one band.

Multispectral Scanner (MSS) - A line-scanning instrument flown on Landsat satellites that continually scans the Earth in a 185 km (100 nautical miles) swath. On Landsats 1, 2, 4, and 5, the MSS had four spectral bands in the visible and near infrared with an IFOV of 80 meters. Landsat 3 had a fifth band in the thermal infrared with an IFOV of 240 meters. The MSS is a non-photographic imaging system that utilizes an oscillating mirror and fiber optic sensor array. The mirror sweeps from side to side, transmitting incoming energy to a detector array that sequentially outputs brightness values (signal strengths) for successive pixels, one swath at a time. The forward motion of the sensor platform carries the instrument to a position along its path where it can image an adjacent swath.