LP DAAC Glossary N through Z

NASA-AFFILIATED INVESTIGATOR. A NASA-Affiliated Investigator is a researcher who has entered into an agreement with NASA for the use of data with the intent to publish research results in scientific literature available to the general public. An affiliated investigator cannot use data pertaining to the agreement for any commercial or government operational purposes.

ORBITAL PERIOD. The time it takes a satellite to complete one revolution or orbit around the Earth. For example, the orbital period of Landsat 7 is approximately 1.5 hours. [NOAA]

PANCHROMATIC. Sensitive to most or all of the visible spectrum between 0.4 and 0.7 micrometers. [NOAA]

PASSIVE SENSOR. Remote sensing instrument that collects radiation that is reflected or emitted by the Earth. For example, the Landsat ETM+ sensor is a passive remote sensor. [NOAA]

POLAR ORBIT. An orbit with its plane aligned parallel with the polar axis of the Earth. [NOAA]

RADIOMETER. Device that detects and measures electromagnetic radiation. [NOAA]

RESOLUTION. A measure of the amount of detail that can be seen in an image. The size of the smallest object recognizable using the detector. [NOAA]

SPECTRAL RESPONSE. The relative amplitude of the response of a detector versus the frequency of incident electromagnetic radiation. [NOAA]

SIS--SPHERICAL INTEGRATING SOURCE. An SIS is a hollow sphere with the entire inner surface uniformly coated with a material which has a high diffuse reflectance. The basic concept behind the spherical shape is that light from the internal source has a chance to perform multiple bounces, thereby, randomizing its original direction before it exits a small aperture. A perfect diffuse reflector can behave like a perfect (i.e., Lambertian) diffuse source which means energy is distributed in all directions equally. A Lambertian source is a source whose radiance is independent of viewing angle. Radiance is defined as the energy flux per unit projected area per unit solid angle leaving a source, or a surface. [Landsat 7 Science Data Users Handbook]

SUN-SYNCHRONOUS ORBIT. An orbit in which a satellite is always in the same position with respect to the rotating Earth at the same time of day. [NOAA]

SYNOPTIC VIEW. The ability to see large areas at one time, such as an entire metropolitan area. [NOAA]

TM--THEMATIC MAPPER. The Landsat TM sensor is a nonphotographic imaging system which utilizes an oscillating mirror and seven arrays of detectors which sense electromagnetic radiation in seven different bands. The TM sensor, a derivative of the multispectral scanner generation of sensors, achieves greater ground resolution, better spectral separation, improved geometric fidelity, and greater radiometric accuracy and resolution. [Landsat 4 Data Users Handbook]

THERMAL INFRARED. Electromagnetic radiation with wavelengths between 3 and 25 micrometers. [NOAA]

VISIBLE RADIATION. The electromagnetic radiation that humans can see as colors. The visible spectrum is made up of wavelengths between 0.4 to 0.7 micrometers. Red is the longest and violet is the shortest. [NOAA]