Aerial photography vs RS satellite


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Aerial photography vs RS satellite

  1. 1. Aerial Vs Satellite Remote SensingAerial PhotographyTaking aerial photographs of the Earths surface is a passive form of remotesensing generated from cameras mounted on aircraft, satellites and otherspacecraft. The photographs are taken every 10 to 30 seconds as an aircraftfollows a systematic overlapping flight pattern at a fixed altitude. Each pictureslightly overlaps the preceding picture so that a stereoscopic (3-D) image of theentire area can be produced and ground objects can be more easily interpreted(note that a strict set of mathematical corrections are applied in anaerotriangulation process prior to compilation to remove errors such asatmospheric refraction, film shrinkage, and underwater refraction). NOAAsprimary aerial photographic product is a 9x9 inch color photograph, which isusually exposed at scales from 1:10,000 to 1:50,000. NOAA photographers canalso capture images from select parts of the electromagnetic spectrum by usingvarious combinations of films and filters. The types of imagery they usually collectinclude natural color, panchromatic (black-and-white), and false-color infraredand black-and-white infrared photography.Since the late 1930s, precision aerial photography has been the primary datasource for coastal survey maps, shoreline feature delineation maps, nauticalcharts and other agency coastal geographical information systems. Unfortunately,however, aerial photography has limitations in that it can only provide highresolution spacial imagery when weather (e.g., cloud cover, sun angle) andenvironmental (e.g., tidal) conditions are optimal.Furthermore, the spectral sensitivity of aerial photography is limited to smallrange from about near ultraviolet to near infrared. Therefore, Space agencies iscurrently investigating existing and new remote sensing technology to augmentand/or replace conventional aerial photgrammetry. Unlike traditional aerialphotography, these techniques are able to capture images derived from a muchbroader portion of the electromagnetic spectrum (from low-frequency radiowaves through gamma-ray regions of the spectrum) and in some cases are notrestricted by time of day, weather conditions, and other environmentalanomalies.S K Diwakar
  2. 2. Aerial Vs Satellite Remote SensingSatellite Remote Sensing Remote sensing is the science of remotely acquiring, processing, interpreting and presenting spatial data for objects and environmental processes using signals from a broad range within the electromagnetic spectrum. Remote sensing instruments are able to produce images of the physical properties and characteristics of objects without being in physical contact with them. Instead, this highly advanced technology forms images by gathering, focusing, and recording reflected light from the sun, energy emitted by the object itself, or reflected radar waves (which were emitted by the satellite or other remote sensing devices). Therefore, remote sensing can be further characterized as either “passive” or "active." Passive remote sensing detects available (background) electromagnetic energy from natural sources (such as sunlight), while active remote sensing, depends on an artificial "light" source (such as radar) to illuminate the scene. NOAA uses digital photogrammetric work stations to produce numerous remote sensing products, including shoreline vectors and maps, digital elevation models, digital terrain models, airport layout diagrams, aviation obstruction charts, and various other special use maps and products. Furthermore, more advanced remote sensing technologies can be less expensive than collecting the same type and quantity of data using aerial photography and conventional ground survey techniques. Satellite Imagery vs. Aerial Photography Satellite imagery is an alternative to aerial photography but there is a lot of confusion as to what is actually satellite and what is aerial photography. Many people think that the data seen in Google Earth is taken from a satellite when in reality it is high resolution digital aerial photography. Similarly, many television shows, such as the BBCs Spooks, refers to theirS K Diwakar
  3. 3. Aerial Vs Satellite Remote Sensing imagery of towns and cities as satellite data when it is actually aerial data photography supplied by Bluesky! So, what are the main differences between the two and which would be most suited to your project? Below is a list of benefits and weaknesses for both aerial photography and satellite imagery. This information should help you make an informed decision is on the type most suited to your requirements. Satellite imagery Aerial photography Speed Speed Satellites are capable of collecting Aerial photography used to be a large amounts of data in relatively slow and time consuming process. small amounts of time. A modern The amount of time taken to satellite can be moved into position in capture an area depends greatly on less than 3 days and can take the its size and shape. As airplanes fly photographs quickly once locked on to back and forth in runs a series of an area. The size of these pictures are overlapping photographs are taken. very large and allow the complete area The dawn of digital aerial to be captured using less images and photography cameras has made the therefore, in a shorter space of time. acquisition of airborne This is necessary with satellites as, photography considerably quicker. because of their limited numbers, the However, the newest cameras are satellite may be required in a different making this faster still by location very soon after. recording strips of data rather than individual frames. Level of detail Level of detail Satellites generally reside several Aerial photography has the hundred kilometers above the earths distinct advantage of having the surface. Although satellite imagery has lens closer to the subject, in this improved greatly over the years it is case the land. By adjusting the still lower resolution than aerial flying height of the aircraft photography. High resolution satellite capturing the data it is possible to imagery as high as 50cm per pixel is improve the detail that can be readily available, up to 41cm in the case captured. Most aerial photography photogra of GeoEye-1 (however, the U.S. 1 was flown with a resolution of Military requires resampling the between 50cm to 12.5cm per pixel. imagery to 50cm for all customers not With the new technology of aerialS K Diwakar
  4. 4. Aerial Vs Satellite Remote Sensing explicitly granted a waiver by the U.S. photographic cameras it is not Government). Military satellites more t). unusual for newer imagery to be than likely have a higher resolution but captured at 10cm per pixel. In as yet this imagery has not become some cases this can be as low as publically available. Most off-the-shelf off 5cm or 2.5cm per pixel. Ho However, satellite imagery is between 250m and these ultra-high resolution high 50cm in resolution. datasets consume enormous amounts of storage space and consists of many times the number of photographs than lower resolution datasets. Also, having a lower flying height enables airborne acquired multi-spectral multi and hyperspectral data to maintain spectral a higher resolution increasing its potential uses. Weather conditions Weather conditions Both satellite imagery and aerial Although aerial photography can photography can suffer from be affected by adverse weather environmental conditions. Being higher conditions there is still the up in the atmosphere means that osphere possibility of photographing areas satellites have more weather in thin or high level cloud which n conditions to cope with. Thin cloud that might stop the use of satellites. may not stop aerial photography can This has a small bearing on the still have a large effect on the quality quality of the final imagery and can of satellite imagery. Due to its position normally be rectified during the in orbit, and other requirements for post-processing stage. There are processing different areas the satellite may be reas also far more planes available for needed for another, clearer area. In taking aerial photo photographs than this case the window of opportunity for there are satellites so if one plane photography may pass and it may be is needed where the weather is some time before the satellite can be clearer then another may be repositioned. It is worth noting that available to take its place. RADAR RADAR data is not affected by is cloud penetrating so it is not weather conditions so can be collected itions affected by adverse weather. at any time.S K Diwakar
  5. 5. Aerial Vs Satellite Remote Sensing Types of data Types of data Many modern satellites can collect a Most aerial acquisition aircraft are variety of data. These include standard fitted with a mount that allows a photographic imagery, colour infrared number of different cameras or and in some cases LiDAR thermal, LiDAR, sensors to be attached to the radar data. This variety of datasets o same aircraft. This allows the makes satellites very versatile. swapping of capture devices but However, non-standard data sources standard only when the plane is not airborne. he such as thermal, LiDAR, multi multi-spectral Some aircraft can mount multiple and hyperspectral imagery will likely be cameras or sensors and some of expensive to capture or may not even the latest aerial cameras capture be publically available. The main different types of data problem with satellite dat types is data simultaneously, such as standard that when new or improved technology imagery, radar and colour infrared. is released it is very difficult to Other datasets such as thermal change the sensors and cameras in a imaging requires the flying to be satellite but in a plane or helicopter it performed at night so a plane that is simply a case of removing the old was capturing standard imagery device and replacing it with the new during the day can be converted one. during the evening and then sent out again at night to capture thermal data. Having a removable sensor allows aerial acquisition to keep abreast of the latest developments in new technologies and the cost of fitting these is much lower than in satellites orbiting many miles in orbit. Location Location The major advantage of satellite satellit Location can cause a delay for imagery is that the satellite can be aircraft acquisition teams. To positioned to take imagery of anywhere guarantee that the survey can be on the planet. It does not have to cross completed an acquisition team borders or go through the many must remain on stand-by near to stand passport controls that could delay a the area to ensure that a weather visiting acquision team. Being above the window is not missed. Luckily there earth, it is more efficient for a are many aerial companies aro aroundS K Diwakar
  6. 6. Aerial Vs Satellite Remote Sensing satellite to allow the earth to revolve the world who specialize in below it than to physically move to the photographing their own country. necessary location. Satellites still need This means that for a company in to take into account the location of the Australia to acquire photography sun to acquire visible light surveys so of the UK they only have to many satellites try to remain in sun sun- contact one of the companies that synchronous orbit. specialize in data of that area. Post-processing Post-processing Imagery acquired by satellite usually Early aerial photography was made consists of far fewer "shots" than that up of tens of thousands of taken by aircraft. The extra distance individual photographs. When the means that more area can be covered aerial photography industry in one pass - at the deficit of detail. adopted digital cameras each Satellites usually capture data in strips digital file was a copy of what was (similar to a continua video of the continual captured using analogue cameras. area) and allow a larger amount of data Recent developments in aerial to be acquired per digital file. This camera design have moved away requires far less post-processing than post from these traditional images and if it were to capture individual "frame" moved towards the satellites images. method of capturing strips of imagery instead. This has greatly reduced the amount of post- post processing work required but, with its lower flying height, there are still more images than with the higher flying satellites.S K Diwakar