- LIDAR
LIDAR, which stands
for Light Detection and Ranging, is a remote sensing method that
uses light in the form of a pulsed laser to measure ranges (variable distances)
to the Earth. These light pulses—combined with other data recorded by the
airborne system— generate precise, three-dimensional information about the
shape of the Earth and its surface characteristics.
A LIDAR instrument principally
consists of a laser, a scanner, and a specialized GPS receiver. Airplanes
and helicopters are the most commonly used platforms for acquiring LIDAR data
over broad areas.
LIDAR systems allow scientists
and mapping professionals to examine both natural and manmade environments
with accuracy, precision, and flexibility. NOAA scientists are using LIDAR
to produce more accurate shoreline maps, make digital elevation models for use
in geographic information systems, to assist in emergency response operations,
and in many other applications.
Extra Reading
LIDAR (Light Detection and
Ranging) is an optical remote sensing technology that measures properties of
scattered light to find range and/or other information of a distant target.
LIDAR data is often collected by
air, such as with this NOAA (National Oceanic and Atmospheric Administration) survey
aircraft (top) over Bixby Bridge in Big Sur, Calif. Here, LIDAR data reveals a
top-down (bottom left) and profile view of Bixby Bridge. NOAA scientists use
LIDAR-generated products to examine both natural and manmade environments.
LIDAR data supports activities such as inundation and storm surge modeling,
hydrodynamic modeling, shoreline mapping, emergency response, hydrographical
surveying, and coastal vulnerability analysis.
Radiometry & Photometry
An overview of the science of
measuring light
Radiometry is the science of measuring light in any portion of the
electromagnetic spectrum. In practice, the term is usually limited to the
measurement of infrared, visible, and ultraviolet light using optical instruments.
Irradiance is the intensity of light and is measured in watts per square meter.
Photometry is the science of measuring visible light in units that
are weighted according to the sensitivity of the human eye. It is a
quantitative science based on a statistical model of the human visual response
to light - that is, our perception of light - under carefully controlled
conditions. The photometric equivalent of Radiance is called Illuminance and is
measured in Lumens per square meter (Lux)The human visual system responds to
the light in the electromagnetic spectrum with wavelengths ranging from 380 to
770 nanometers (nm). We see light of different wavelengths as a continuum of
colors ranging through the visible spectrum: 650 nm is red, 540 nm is green,
450 nm is blue, and so on.
Photographic interpretation is
“the act of examining photographic images for the purpose of
identifying objects and judging their significance” (Colwell, 1997). This
mainly refers to its usage in military aerial reconnaissance using
photographs taken from reconnaissance aircraft..
Thermal imaging is a
method of improving visibility of objects in a dark environment by detecting
the objects' infrared radiation and creating an image based on that
information.
Thermal imaging,
near-infrared illumination, low-light imaging and are the three most
commonly used night vision technologies.
Unlike the other two methods, thermal imaging works in environments without any
ambient light. Like near-infrared illumination, thermal imaging can penetrate obscurantist such as smoke, fog and haze.
Extra reading
Here's a brief
explanation of how thermal imaging works: All objects emit infrared energy
(heat) as a function of their temperature. The infrared energy emitted by an
object is known as its heat
signature. In general, the hotter an object is, the more radiation it
emits. A thermal imager (also known as a thermal camera) is essentially a heat
sensor that is capable of detecting tiny differences in temperature. The device
collects the infrared radiation from objects in the scene and creates an
electronic image based on information about the temperature differences.
Because objects are rarely precisely the same temperature as other objects
around them, a thermal camera can detect them and they will appear as distinct
in a thermal image.
