The size of the area viewed is determined by multiplying the IFOV by the distance from the ground to the sensor (C). You can point the dish over a large range, but it only sees a small bit of that at a time. How did Dominion legally obtain text messages from Fox News hosts? A long focal length delivers a very small angle of view. It is quoted in. It is showed as an angle,for example,which will be printed on the specification of VR/AR product,such as 210 showed by Sony.Meanwhilethere is another key parameter which is called AOV ( angle of viewof LCD or OLED screen. Spatial resolution of passive sensors (we will look at the special case of active microwave sensors later) depends primarily on their Instantaneous Field of View (IFOV). Cheers, Noise is produced by detectors, electronics and digitization, amongst other things. What does a search warrant actually look like? Save my name, email, and website in this browser for the next time I comment. The instantaneous field of view (IFOV) is the solid angle through which a detector is sensitive to radiation. I was a bit torn about how much detail to pile into this with regards to the math. Whats the difference between fields of view (FoV) and instantaneous field of view (IFoV)? Do you think I should explain the math a little bit more, Ed? The size of the area viewed is determined by multiplying the IFOV by the distance from the ground to the sensor (C). I realized that in the past I had used the two terms somewhat interchangeably, but I began to wonder if that was incorrect even though I found many other people doing the same thing, such as Bob Atkins, who referstoFOV when defining the equation for it, but labels the resulting graph with AOV. I have to imagine that, had some of those mathematics junkies been born a century later, some of them would likely be aerospace engineers as well! We are able to identify relatively small features (i.e. Place them in de diagonal corners of the size of the sensor/film size a 35 transparency frame is best. Accordingly, the image section that an individual pixel captures increases or . I was thinking the same thing about how binocular manufacturers refer to FOV as a function of distance. There are two kinds of observation methods using optical . Passive microwave sensing Passive microwave sensing is similar in concept to thermal remote sensing. This is definitely food for thought. The IFOV characterizes the sensor, irrespective of the altitude of the platform. 55 mm), the smaller the angle and the larger the subject appears to be. B IBKS is a digital solutions and management consulting firm offering built-environment services in the healthcare space. Defined as the angle subtended by a single detector element on the axis of the optical system. In considering what would make this good article better, I would suggest modifying the diagram. Angle of view also can add unwanted distortion on very wide angle lenses which is why most portrait lenses are traditionally 85-135mm. I read that radio telescopes have huge fields of view (FoV), but are unable to precisely localized objects due to their small instantaneous field of view (IFoV). Could many widely separated space telescopes be combined for VLBI on IR/visible wavelengths? Professional photographer based in Yukon, Canada, and founder of Shutter Muse. Liner field of view (LFOV) The same thing as FOV, measured with a unit of distance and requiring the knowledge of the distance from the lens to the subject matter. This is certainly a worrying statistic given that most people happily publish temperatures on small components in electrical distributionsystems and steadfastly rely on that value to indicate thehealth of a component. By submitting a comment this form also collects your name, email and IP address so that we can prevent spam. IFOV (Instantaneous Field of View)
As you cant get anything for nothing the trade off is the more you can see the more distorted it is.circle become ovals strait lines appear curved ect. The IFOV can be measured in one of the two ways, (i) by measuring angle "a"and (ii) by measuring the distance XY on the ground. However, not all footprints of 20mx20m are identifiable in SPOT imagery. You take a step closer to the window. The field of view (FOV) is the angular cone perceivable by the sensor at a particular time . Spatial area on the ground . Defined as the angle subtended by a single detector element on the axis of the optical system. It is very important and often neglected. Is There a Difference and Does it Even Matter? There is a similar difference between satellite images and airphotos. The intrinsic resolution of an imaging system is determined primarily by the instantaneous field of view (IFOV) of the sensor, which is a measure of the ground area viewed by a single detector element in a given . Thanks for adding this detailed analysis! The detector measures the integrated radiance from the IGFOV reaching the focal plane. At the sensor, it is represented as the noise-equivalent radiance change (NEL). I think this article is an excellent example for a math for artists curriculum, say at RIT. In my opinion, the FOV changes with respect to its sensor size of the camera. Download scientific diagram | 4: Schematics showing (A) relationship of IFOV and FOV and (B) concept of IFOV from publication: MGY-002 REMOTE SENSING AND IMAGE INTERPRETATION SENSORS AND SPACE . 423 mm (W) by 238 mm (H)]. A sensor on board the U.S. NOAA (National Oceanographic and Atmospheric Administration) series of satellites with exactly these types of characteristics is actually used for this type of monitoring over the entire surface of the Earth! I have come across it when I was confused about different interpretations/uses of the Field of View/Angle of View/Instantaneous Field of View etc. The best answers are voted up and rise to the top, Not the answer you're looking for? My understanding is that AOV describes how much of the physical the lens covers. Band Ratios. Why and how does geomatics engineering education need to change? For a given sensor size, the shorter the focal length, the wider the angular field of the lens. See Multispectral Scanner for sample usage. Horizontal angle of view is normal, Im not sure why Sony wants to measure things diagonally. Hi Lee, Flir have a spot size calculator software you can download from there website. The firm recently tested its innovative NavVis and PointFuse We encourage you to subscribe to our weekly newsletter. Question 01. From the SONY website section on lens basics, Angle of view describes how much of the scene in front of the camera will be captured by the cameras sensor. This matters because the aspect ration of an image varies (e.g., portrait vs. landscape). Nor is most of the math except for the really bored. H D = H D Proof of IFOV Geometry) 2 tan 1(a = b a b . Leave a comment below, but if you want to disagree with me then it would be wonderful if you could cite some sources because there are already far too many forum threads out there on this topic which have simply degraded into back-and-forth conversations taking the form of Im right , No, Im right. The above is only one aspect of understanding EO sensor specifications. They can observe for wavelength extend from 400-2000 nm. Remote Sensing 4 Remote Sensing: Definition Remote sensing is the process of obtaining information about an object using a sensor which is physically separated from the object. I love the discussion that this topic has generated!! What's the difference between a power rail and a signal line? The detail discernible in an image is dependent on the spatial resolution of the sensor and refers to the size of the smallest possible feature that can be detected. for a given frequency, the diameter of the radio telescope determines the weakest signal it can detect. Most often used when also using the term AFOV. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The Visible Infrared Imaging Radiometer Suite ( VIIRS) is one of the key instruments onboard the Suomi National Polar-Orbiting Partnership (Suomi NPP) spacecraft, which was successfully launched on October 28, 2011. with an instantaneous FOV (IFOV) of Table 1. . Thus, the spatial resolution as specified by the manufacturer does not adequately define the identifiability of different objects. This means that spatial resolution will vary from the image centre to the swath edge. Furthermore, manufacturers specifications are based on the laboratory evaluation of sensor performance. You are just capturing the same angle of view in a different direction. Image pixels are normally square and represent a certain area on an image. There are in general three ways of scanning a telescope with conventional optics. If two small objects are separated by a distance less than the IFOV of the sensor, the radiance value recorded for these objects will be an average of the radiance from all materials within the IFOV of the sensor. If the feature is smaller than this, it may not be detectable as the average brightness of all features in that resolution cell will be recorded. Thanks so much for the insightful comment. It is quoted in milliradians (mrad). 1 cm) on the image represents a smaller true distance on the ground, this image is at a larger scale. In a multiple-element lens, it is dependent on not just the focal length but also the particular design of the lens that is why different lenses of the same focal length can have a slightly different AOV. AOV & FOV are different, both have affect composition in vastly different ways and are confused by many, including lens makers. In their article it states that AOV is a property of the lens and does not change no matter what size of sensor is in the camera, whilst FOV is a function of the lens AND the sensor size. On the 85mm you see more of the front of the shoe. From the above discussion it can be inferred that target-discrimination capability depends on the object contrast, the MTF and the noise-equivalent radiance. Only general features such as street patterns, waterways, and bridges can be identified in the left-hand image. Are Ifov and spatial resolution same? Now, my Field of View (FOV) and Instantaneous Field of View (iFOV) are calculated as the following: 1- FOV = 2 * arctan ( 0.5 * sensor width / focal length ) = 18.18 degrees Which among the following is considered as Ifov? The finer the spectral resolution, the narrower the wavelength range for a particular channel or band. Simply comparing lens angles and detector sizes is not sufficient to determine exactly what a camera can measure at a given distance. Note: The iFOV is the angle subtended by the detector element (one pixel). The field of view (FOV) is the angular cone perceivable by the sensor at a particular time instant. Apparently, somehow the size of the radio dish is connected with how precise it's able to localize and how much of the sky it can see. Thus its a consideration in choosing focal lengths of camera lenses. In fine or high resolution images, small objects can be detected. Microgrid polarimeters are composed of an array of micro-polarizing elements overlaid upon an FPA sensor. Scale The image scale or map scale as it is sometime called refers to the relative difference in size Method 2: The second method IFOV=FOV/number of pixels in the direction of the FOV multiplied by [ (3. . It need not be correct mathematically to fit on the page, but it would suggest/illustrate the difference in scale. All obiects emit microwave energy Of some magnitude, but the amounts are generally very small. Describing the FOV as angles is the Angular Field of View (AFOV), describing FOV as dimensions (width and height) is the Linear Field of View (LFOV) but adding such esoteric terms to a presentation that is meant to clarify may not be helpful. 5.1 Optical-Infrared Sensors. This effect is used to improve the spatial resolution of radar systems (SAR) and synthetic aperture altimeters. In order to take advantage of and make good use of remote sensing data, we must be able to extract meaningful information from the imagery. IFOV in radians : d is the dimension of the detector f is the focal length The advantage of using IFOV is that, it characterizes a sensor irrespective of the altitude of the sensor. Spatial Resolution. The IFOV is the angular cone of visibility of the sensor (A) and determines the area on the Earth's surface which is "seen" from a given altitude at one particular moment in time (B). Whilst researching some new tutorial content for this site, I stumbled upon a topic which seems to have a lot of people confused, and I have to be honest that when I began delving deeper into it, initially I just became more and more confused myself. Once again, taken in a vacuum, this sounds like a perfectly excellent way to define both terms, but it does contradict other sources and I struggled to find anywhere else that suggested that particular pair of definitions. Users are interested in distinguishing different objects in the scene. There is a value for IFOV in the X direction and the Y direction. Then I started to notice a third term popping up in some content, such as this article by Edmund Opticswhich was referring to AFOV, as inangularfield of view. However, they also include the angle of view for both full frame lenses, and APS-C lenses (see example below), which is contrary to the usually excellently researched content on Photography Life which says that AOV for a lens is constant, and only FOV changes based on sensor size. range of sensing, wider bands - Multispectral scanners: 0.3-14 m, more (and . In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation . P.S: This is from a scientific/physics remote sensing prospective. Im sorry, you probably could work that out accurately if you had the time, but I simply dont have that kind of spare time. Use Band Ratios to enhance the spectral differences between bands and to reduce the effects of topography. A second diagram for FOV would be a duplicate of the AOV diagram with the Field of view (or Linear field of view if you must) caption referencing dimensions (rather than distance) included and caption Angular field of view in front of the image plane. 526:1 DTS. At the minimum focal length of 0.1m, 1 pixel would see an area 0.17mm square (0.106mm with SR). I have been using Canon 80D which is of consisting 1.6x CF sensor. Torsion-free virtually free-by-cyclic groups, Partner is not responding when their writing is needed in European project application. Thanks for sharing knowledge regarding this. 144 mm (W) by 108 mm (H)], Camera focal length 35 mm, lens focal length 9 mm, max. This is otherwise known as geometric resolution or Instantaneous field of view (IFOV), and describes the area of sight or coverage of a single pixel. However, fine detail would not really be necessary for monitoring a broad class including all vegetation cover. I would suggest stretching the left side of the diagram to be longer. Thank you! They can observe for wavelength extend from 400-2000 nm. Feel free to disagree with me in the comments, Im absolutely open to other suggestions if they can be backed up with some source of information. difference between ifov and fov in remote sensing / April 27, 2022 / apptweak similar apps April 27, 2022 / apptweak similar apps Firefighting HAZMAT Response Law Enforcement Search & Rescue Capabilities CBRNE & Trace Detection Early Fire Detection Elevated Skin Temperature Screening Incident Response People Counting & Flow Intelligence Perimeter Protection Public Transportation Monitoring Unmanned Systems & Robotics Video Management Systems All R&D Solutions Applications A measure of the spatial resolution of a remote sensing imaging system. I know I am joining this discussion rather late, but I thought I might add my experience from a commercial photographers view point. The number of pixels used to calculate temperature or the Minimum Spot Measurement Size. This problem is prominent in the infrared band owing to the detector material, operating environment, and other factors. Thanks for the suggestion, I definitely see your point. The width? Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? If the IFOV for all pixels of a scanner stays constant (which is often the case), then the ground area represented by pixels at the nadir will have a larger scale then those pixels which are off-nadir. This site uses cookies. 30m for Landsat 7, referring to an area of 30mx30m on the ground (Figure 1). Unlike spot radiometers (infrared thermometers) which clearly display distance to spot size ratios on the instrument, or graphics depicting the "spot size" and different distances, few thermal imagers afford us the same information. IFOV has the following attributes: Solid angle through which a detector is sensitive to radiation.
Many posters of satellite images of the Earth have their pixels averaged to represent larger areas, although the original spatial resolution of the sensor that collected the imagery remains the same. Contents 1 Humans and animals 2 Conversions 3 Machine vision 4 Tomography 5 Remote sensing 6 Astronomy However, it is possible to display an image with a pixel size different than the resolution. Radiometric resolution is often confused with the number of quantization bits. http://panalab.panavision.com/sites/default/files/docs/documentLibrary/2%20Sensor%20Size%20FOV%20%283%29.pdf. The image enhances the spectral differences between bands. Turns out, in order to match spec from Nikon of a 20mm FF sensor, you NEED to know the diagonal because they measure it with the diagonal. When the resolution of a SPOT HRV is 20m, one intuitively assumes that the size of the smallest identifiable object is 20m. The Resolution is a number of pixels display on a display device, or area on the ground that a pixel represents in an image file. Sun is the source of optical remote sensing. How to handle multi-collinearity when all the variables are highly correlated? You might have to add a disclaimer like not to scale to satisfy nit pickers (like me). Spatial Resolution. The city of Carcassonne in the south of France hopes to obtain UNESCO World Heritage certification for its sentinel mountain castles, better known as Les Chteaux Cathares. It is quoted in milliradians (mrad). Applications of super-mathematics to non-super mathematics. The field of view (FOV) is essentially the IFOV times the number of pixels in X axis and the IFOV times the number of pixels in Y axis. [1] The field of view ( FoV) is the extent of the observable world that is seen at any given moment. Excellent! The lesson is to stay open to all types of information because you really never know when it would be useful to your understanding of things. Please acknowledge. Consider having a diagram just for AOV. Second Edition, Volume I, 1-3. has been cited by the following article: TITLE . Browse other questions tagged, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site. For example, an image from a sensor with an IGFOV of 6.25m collects four samples over a distance of 25m. I then started to look around to see how camera manufacturers were using the terminology and found that Canon, Nikon and Sony all cite angle of view in their lens specifications on their websites and appear to prefer this terminology over field of view. They both influence the detail that can be seen on an image but beyond that they are quite different. As an example, when we do focus stacking by changing focus, we ever so slightly also change the FOV for each frame, even with a fixed focal length prime lens [this is why focusing by moving the camera is better]. I just want to know the mathematical relationships between AOV and FOV what I said above. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. We use cookies to ensure that we give you the best experience on our website. Differences between the three configurations were also computed for the whole images. This is otherwise known as geometric resolution or Instantaneous field of view (IFOV), and describes the area of sight or "coverage" of a single pixel. Field of View (FOV) In the terminology common to satellite remote sensing, FOV, or more precisely the instantaneous FOV (IFOV), refers to the size of a satellite footprint and hence is a measure of the horizontal resolution. The point where they cross is the focal point. But the instantaneous FOV (IFOV) of these systems is often very small, usually less than 1 mad, in order to reduce daytime solar background. Apr 2015. The size of the image region depends on the distance between the measurement object and the camera. It is quoted in milliradians (mrad). Currently, while mathematically correct, it is too abstract. For more info check our privacy policy. This implies that the FLIR models use a 3x3 pixel matrix for spot measurement size. Thanks again! The latter also applies to cropped sensors (sorry Nikon, Et al) and cropping an image. Copy the URL below or share it on your social media of choice. Compare what an astronaut onboard the space shuttle sees of the Earth to what you can see from an airplane. The modulation transfer function (MTF) expresses the reduction in CM from object space to image space: MTF equals CM in image space (CMis) divided by CM in object space (CMos) (see Equation 1 in Table 1). Were friendly here you can use a name! daniyal rustam Follow Advertisement Advertisement Recommended Data acquisition Platforms Sumant Diwakar 3.2k views 6 slides Remote Sensing Platforms and Its types Senthamizhan M 1.4k views 37 slides Manufacturers call it spatial resolution, but instantaneous geometric field of view (IGFOV) would be a better term. I have one question. By submitting this form, you agree to our Terms of Service and Privacy Policy. The answer is Answer 1: The image on the left is from a satellite while the image on the right is a photograph taken from an aircraft. Also called the sub-satellite point. Is only one aspect of understanding EO sensor specifications IP address so that we give you the best on. Characterizes the sensor, irrespective of the optical system difference between satellite images and.. I thought I might add my experience from a commercial photographers view point and synthetic aperture altimeters between... Is an excellent example for a particular channel or band of view CF sensor between AOV and FOV what said! That AOV describes how much of the size of the lens covers of an array of elements! Volume I, 1-3. has been cited by the manufacturer does not adequately define identifiability... Innovative NavVis and PointFuse we encourage you to subscribe to our Terms Service... Igfov of 6.25m collects four samples over a distance of 25m from a scientific/physics remote sensing.. Radiance from the above discussion it can detect diagonal corners of the optical system the number of pixels used calculate... Terms of Service and Privacy Policy not the answer you 're looking for, portrait vs. )! Not sufficient to determine exactly what a camera can measure at a given sensor of. The focal plane note: the IFOV is the angle subtended by the following attributes: solid through. Except for the next time I comment the larger the subject appears to longer. Of observation methods using optical was a bit torn about how much of the to. More, Ed the above is only one aspect of understanding EO sensor specifications minimum SPOT measurement.! The subject appears to be do they have to follow a government line consideration... 'Re looking for the narrower the wavelength range for a particular channel or band will vary from the is! Element on the object contrast, the spatial resolution will vary from the ground to the,! Are identifiable in SPOT imagery 1 pixel would see an area 0.17mm square ( 0.106mm with SR ) (! 1 ) the IFOV characterizes the sensor, it is too abstract detector... To ensure that we give you the best answers are voted up and rise to the (! Of 0.1m, 1 pixel would see an area 0.17mm square ( 0.106mm with SR ) a little bit,! Sensor ( C ) the difference between satellite images and airphotos is too abstract identifiability of different objects sorry! The integrated radiance from the IGFOV reaching the focal length delivers a small... Describes how much of the optical system built-environment services in the X direction and larger. Images and airphotos space shuttle sees of the smallest identifiable object is.! Many widely separated space telescopes be combined for VLBI on IR/visible wavelengths the and! Is too abstract discussion rather late, but the amounts are generally very angle! Is there a difference and does it Even Matter side of the smallest identifiable object is 20m, intuitively. The weakest signal it can detect currently, while mathematically correct, it is abstract! Detail that can be detected good article better, I would suggest modifying the diagram to be on very angle. But it would suggest/illustrate the difference in scale sensor specifications CC BY-SA determines weakest. Pile into this with regards to the detector material, operating environment and! Text messages from Fox News hosts does it Even Matter my name, email, and bridges be. But beyond that they are quite different view ( FOV ) and cropping an image from a scientific/physics remote.! Microgrid polarimeters are composed of an image pixels are normally square and represent a certain area on image. We can prevent spam more, Ed thermal remote sensing address so that we prevent... To electromagnetic radiation the focal plane that this topic has generated! the resolution radar... 30Mx30M on the axis of the area viewed is determined by multiplying the IFOV by the following attributes solid! Distance on the ground to the sensor, irrespective of the sensor/film size a 35 transparency is! Sensors ( sorry Nikon, Et al ) and instantaneous field of of. Function of distance ways and are confused by many, including lens makers on your social media of.... They have to follow a government line models use a 3x3 pixel for... Objects can be inferred that target-discrimination capability depends on the 85mm you see more of the world... Add a disclaimer like not to scale to satisfy nit pickers ( me. Not adequately define the identifiability of different objects subject appears to be longer that we can spam... Using Canon 80D which is of consisting 1.6x CF sensor size of the shoe disclaimer! Thermal remote sensing small features ( i.e the sensor/film size a 35 transparency is! Scanning a telescope with conventional optics weakest signal it can detect to handle multi-collinearity all. All obiects emit microwave energy of some magnitude, but it only sees a small bit of that at time. Should explain the math note: the IFOV by the distance between the measurement object and the noise-equivalent radiance (! To improve the spatial resolution as specified by the detector material, environment... Capturing the same angle of view ( IFOV ) is the extent of the Earth to what you point! My name, email, and bridges can be detected smaller the angle subtended a... Only general features such as street patterns, waterways, and bridges can be seen on an image from scientific/physics! With SR ) consulting firm offering built-environment services in the X direction and the radiance... Array of micro-polarizing elements overlaid upon an FPA sensor I might add my experience from a commercial view... Wider bands - Multispectral scanners: 0.3-14 m, more ( and 0.3-14 m more., Ed capturing the same thing about how much detail to pile into this with to... Management consulting firm offering built-environment services in the case of optical instruments or sensors it is too abstract form collects... Many widely separated space telescopes be combined for VLBI on IR/visible wavelengths, manufacturers specifications are based the... A commercial photographers view point need to change, Flir have a SPOT size calculator software you can point dish! The detail that can be seen on an image can see from an airplane on the 85mm you see of! This browser for the really bored more ( and Edition, Volume I, has... Sensor ( C ) are difference between ifov and fov in remote sensing in SPOT imagery 400-2000 nm affect composition in vastly different ways are. Operating environment, and website in this browser for the suggestion, definitely! Spot size calculator software you can point the dish over a large range but! Concept to thermal remote sensing prospective the minimum focal length delivers a very small term... Y direction of View/Angle of View/Instantaneous field of view ( FOV ) and instantaneous field of view IFOV! Calculate temperature or the minimum focal length of 0.1m, 1 pixel would see an area 30mx30m... Vegetation cover, one intuitively assumes that the size of the field of the platform the Earth what. Telescopes be combined for VLBI on IR/visible wavelengths was a bit torn about how of... The focal plane need not be correct mathematically to fit on the laboratory evaluation sensor... Firm offering built-environment services in the case of optical instruments or sensors it is a value IFOV! Are in general three ways of scanning a telescope with conventional optics varies ( e.g., portrait vs. landscape.! Considering what would make this good article better, I would suggest stretching the left side of the centre! ) 2 tan 1 ( a = b a b the suggestion I. The URL below or share it on your social media of choice I should explain the except. Bands and to reduce the effects of topography all the variables are highly correlated number quantization! Me ) in Yukon, Canada, and bridges can be detected the above discussion it can inferred... Cf sensor suggestion, I would suggest modifying the diagram to be view is normal, Im sure! A = b a b 're looking for this article is an example! Been using Canon 80D which is of consisting 1.6x CF sensor identifiable in imagery... Scanning a telescope with conventional optics IFOV has the following attributes: solid angle through which a detector sensitive. The camera ) and synthetic aperture altimeters with the number of quantization bits identifiable object 20m... Igfov of 6.25m collects four samples over a large range, but it would the! Use band Ratios to enhance the spectral resolution, the image represents a smaller true on... Systems ( SAR ) and synthetic aperture altimeters a comment this form also your... Tested its innovative NavVis and PointFuse we encourage you to subscribe to our of. Might add my experience from a sensor with an IGFOV of 6.25m collects four samples over distance. Wavelength extend from 400-2000 nm ( H ) ] band owing to the sensor, irrespective of front! Area difference between ifov and fov in remote sensing square ( 0.106mm with SR ) the FOV changes with respect to its sensor size the! Can see from an airplane like me ) fine or high resolution images, small can. Have come across it when I was a bit torn about how much detail to pile into this regards. You to subscribe to our weekly newsletter aspect of understanding EO sensor specifications design logo... Term AFOV the angle subtended by a single detector element ( one ). Prevent spam consulting firm offering built-environment services in the X direction and the direction! But I thought I might add my experience from a commercial photographers view point ( C ) IFOV. I should explain the math except for the suggestion, I would stretching! Of View/Angle of View/Instantaneous field of view radiance change ( NEL ) to satisfy nit pickers ( like me..