International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004 
  
instantaneous geometric field-of-view (IGFOV): the 
geometric size of the image projected by the detector on the 
ground through the optical system ("pixel footprint). 
interpretability: the ability to identify and distinguish objects, 
features, patterns, and textures within a remote sensing image, 
and determining their significance. It refers to the ability to 
visually examine the image, including object relative locations 
and extents, for a given application (Wolf, 1983). 
Interpretability is related to GSD, SNR, and PSF/MTF, but is 
also subjective in that it is dependent on the judgment/opinion 
of the user and the application. Some methods have been 
developed to evaluate interpretability. 
irradiance: radiant flux per unit area. 
length distortion: the accuracy of distance measures on images 
using a geometric model. 
line spread function (LSF): (a) the |-dimensional PSF 
orthogonal to the length of a thin wire smaller than the system 
pixel size; (b) the derivative of the edge spread function with 
respect te position (Schott 1997). The Fourier Transform of the 
LSF is the OTF in one of the spatial frequency directions. 
linear error-90 (LE90): defines a line which encompasses 90% 
of the points, typically used as an expression of vertical 
accuracy (Z coordinates). 
linearity: the relationship between two variables so that when 
plotted on a graph they yield a straight line (Photonics 
Dictionary 2004) For an imaging system, linearity refers to the 
relationship between the systems digital numbers (DNs) and the 
radiance values measured by the system. The digital number 
recorded by the system should be linearly related to the amount 
of radiance measured by the system. Linearity (or non-linearity) 
is characterized by measuring the system's response to varying 
radiance levels spanning the system's full dynamic range. 
modulation transfer function (MTF): (1) a measure of an 
imaging system's ability to recreate the spatial frequency 
content of the scene. It is the magnitude of the Fourier 
Transform of the "point spread" and "line spread" functions 
(PSF and LSF); (2) a measure of the spatial quality of an 
imaging system. The modulus of the Optical Transfer Function 
(OTF), normalized such that the first value is unity; (3) the 
reduction in contrast in the image compared to the contrast of 
the objects imaged. MTF is the ratio of the amplitude (peak 
intensity difference) of a signal, as seen by the sensor, to the 
true sinusoidal target amplitude as a function of the spatial 
frequency of the target (CCRS 2004). 
modulation transfer function compensation (MTFC): a post- 
processing image restoration technique that enhances image 
sharpness and increases image noise. 
national image interpretability rating scale (NIIRS): a 10- 
level rating scale that defines the ability to identify certain 
features or targets within an image. The NIIRS defines and 
measures the quality of images and performance of imaging 
systems. Through a process referred to as "rating" an image, the 
NIIRS is used by imagery analysts to assign a number that 
indicates the interpretability of a given image. For example, the 
ability to identify trains or strings of standard rolling stock on 
railroad tracks (not individual cars) would receive a NIIRS 
    
rating of 3, while the ability to identify individual spikes in 
railroad ties would receive a rating of 9. The NIIRS concept 
provides a means to directly relate the quality of an image to 
the interpretation tasks for which it may be used (Pike 1998). 
The NIIRS is traditionally used to evaluate panchromatic 
imagery. The Multispectral Image Interpretability Rating Scale 
(MSIIRS) has been developed to rate multispectral imagery. 
noise: the unwanted and unpredictable fluctuations that distort a 
received signal and hence tend to obscure the desired message. 
Noise disturbances, which may be generated within the remote 
sensing system, or which may enter the system from the 
outside, limit the range of the system and place requirements on 
the signal power necessary to produce useful data/information 
(Photonics Directory 2004). See also signal-to-noise ratio, noise 
equivalent delta radiance, noise equivalent delta temperature, 
and systematic noise as key related parameters. 
noise equivalent delta radiance (NEDL, NEAT): the root 
mean square, or standard deviation of the mean, that produces a 
SNR of 1 reported in radiance (or irradiance) units. This 
assumes that all known systematic errors are first removed. This 
measurement represents the lowest signal that can be measured 
by an instrument, just before the signal falls below the level of 
the noise. (Analytical Spectral Devices). NEDL is also referred 
to as noise equivalent radiance (NEL). This can also be reported 
as the Noise Equivalent Irradiance (NEI), which is the radiant 
flux density (W/em2) required for a system to produce an 
output signal equal to the noise, or the input irradiance at which 
the signal-to-noise ratio is unity (Photonics Directory 2004). 
noise equivalent delta temperature (NEDT, NEAT): in 
thermal imaging systems, the change in temperature that yields 
a signal-to-noise ratio of unity (Photonics Directory 2004). 
optical transfer function (OTF): an equivalent measurement 
of the "point spread function" (PSF) obtained through a two- 
dimensional Fourier Transform consisting of the magnitude and 
phase terms. Like the PSF, it is a measure of the spatial 
performance of an optical system. It includes phase relationship 
between the target and measured signals as well as the 
amplitude change as a function of frequency (CCRS 2004). The 
phase component of the OTF is called the Phase Transfer 
Function (PTF). 
point spread function (PSF): a direct 2-dimensional measure 
of a system's ability to reproduce an infinitely narrow source of 
radiance; thus, the response of a system to a point source of 
radiance. Mathematically: the response to a delta function 
(Schott 1997). PSF defines the apparent shape of a point target 
as it appears in the output image. It is a plot of illuminance of 
the image as a function of distance in the image plane (CCRS, 
2004). See also optical transfer function, modulation 
transfer function, edge transfer function, relative edge 
response, line spread function and spatial out-of-field. 
polarization: the partial orientation of the electric (and 
magnetic) fields of an electromagnetic wave. Horizontal 
(H)/ Vertical (V) polarization refers to the electronic filed 
(magnetic field) vector's being parallel/normal to the surface of 
the medium that the wave is incident upon. Polarization 
knowledge offers an additional capability in detecting object 
characteristics and in discriminating between them, especially 
in the microwave region of the electromagnetic spectrum 
(Kramer 2001). See also polarization sensitivity and Stokes 
     
    
   
  
   
      
   
    
   
  
  
  
  
  
  
  
  
  
  
  
  
  
    
   
  
  
  
  
  
  
  
  
  
  
  
    
    
   
  
  
  
  
   
   
  
  
  
    
   
   
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