Optical cross section (OCS) is a value which describes the maximum amount of
optical flux reflected back to the source. The standard unit of measurement is m
2/sr. OCS is dependent on the geometry and the reflectivity at a particular
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
of an object. Optical cross section is useful in fields such as
LIDAR
Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected li ...
. In the field of
radar
Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...
this is referred to as
radar cross-section
Radar cross-section (RCS), denoted σ, also called radar signature, is a measure of how detectable an object is by radar. A larger RCS indicates that an object is more easily detected.
An object reflects a limited amount of radar energy b ...
. Objects such as
license plates
A vehicle registration plate, also known as a number plate (British, Indian and Australian English), license plate (American English) or licence plate (Canadian English), is a metal or plastic plate attached to a motor vehicle or trailer for ...
on automobiles have a high optical cross section to maximize the laser return to the
speed detector gun.
Flat mirror
Optical cross section of a flat mirror with a given reflectivity at a particular wavelength
can be expressed by the formula
:
Where
is the cross sectional diameter of the beam. Note that the direction of the light has to be perpendicular to the mirror surface for this formula to be valid, else the return from the mirror would no longer go back to it source.
In order to maximize the return a
corner reflector
A corner reflector is a retroreflector consisting of three mutually perpendicular, intersecting flat reflective surfaces. It reflects waves incident from any direction directly towards the source, but translated. The three intersecting surfa ...
is used. The alignment of a corner reflector with respect to the source is not as critical as the alignment of a flat mirror.
Other optical devices
Optical cross section is not limited to reflective surfaces. Optical devices such as telescopes
[{{Cite journal , last1=Han , first1=Yi , last2=Sun , first2=Huayan , last3=Li , first3=Yingchun , last4=Guo , first4=Huichao , date=2013-06-06 , title=Fast calculation method of complex space targets' optical cross section , url=http://dx.doi.org/10.1364/ao.52.004013 , journal=Applied Optics , volume=52 , issue=17 , pages=4013 , doi=10.1364/ao.52.004013 , pmid=23759850 , bibcode=2013ApOpt..52.4013H , issn=1559-128X, url-access=subscription ] and cameras will return some of the optical flux back to the source, since it has optics that reflect some light. The Optical cross section of a camera can vary over time due to the camera shutter opening and closing.
References
Cross section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture and engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**A ...
Lidar