Reader, Dept. of Geology
St. Xavier's College, Mumbai
and Sr. Associate Editor (honorary) GIS Development.
In the new millennium, design and development of airborne cameras has seen a paradigm shift. The historical F24 camera used by the legendary Sydney Cotton on the eve of WW II is just a toy when compared to Airborne Digital Cameras (ADC) of today. The ADCs are equipped with ccd arrays far more efficient than the one invented by Boyle and Smith of Bell Labs in 1969. Just compare the 100 X 100 pixel device commercially produced by Fairchild Semiconductors in 1974 to today's 10560 X 10560 (111Mpixel) ccd array by DALSA. A few of these cameras also use CMOS sensors.
The almost simultaneous launch of the Leica ADS40 and the Z/I imaging DMC in 2000 proved to sceptics that digital imaging technology with sufficient enough resolution has finally been designed for use in aerial cameras. This article is a status report on the standard airborne digital cameras available today for photogrammetry. ADCs can be categorised under three heads based on their frame format. The Small-format frame cameras (< 16Mpixels), the Medium-format frame cameras (< 50Mpixels) and the Large-format frame cameras (> 50Mpixels). This article is an attempt at
Small-format frame Cameras
Single lens monochrome cameras
The Carl Zeiss VOS
The Visual Sensor VOS 40/500 has a 4 mega pixel focal plane CCD array (2,048 x 2,048 pixels) with 12/8 bit digital video output. Equiped with a zoom lens (42 to 500mm), this Fig.1 a. The CZ VOS 40/500 camera in its housing., b. A monochrome aerial photograph taken by CZ VOS 40/500. (www.zeiss.com/optronics) camera was specifically designed for the requirements of the Reccelite Tactical Reconnaissance Pod. Within its class, this camera has a large pixel count, a high frame rate, a good angular resolution and most important – no mechanical shutter which increases its reliability.
Fig.1 a. The CZ VOS 40/500 camera in its housing.
Single lens color cameras with mosaic filters
These are our conventional digital SLR cameras with a single array of CCDs. Their speciality being – ruggedness and the availability of quality interchangable lenses. Mosaic filters allow color images to be generated by Bayer interpolation. Specially designed mounting would be required for these cameras along with accessories like a wireless transmitter to download the images on the fly (literally) to other storage devices. These cameras are excellent for local use where quick monitoring of events is required. Kodak was among the first to introduce these cameras in the 6Mega pixel range – Kodak DCS 460/560/660/760 series.
If these cameras are to be used for any photogrammetric applications then they will need to satisfy the requirements of a 'Metric Camera' viz. Fixed focal length, known lens distortion and known position of principal point relative to the sensor elements
The Canon EOS-1Ds Mark II and the Nikon D2X
The Canon EOS-1Ds Mk II equiped with the legendary Canon lens quality, this pocket sized dynamite with its 16 mega pixel CMOS sensor, actually can qualify as a low-end medium format frame camera. The Nikon D2X is equiped with a 12.4 mega pixel CMOS sensor.
The GeoTechnologies SF-DMC
This small format 3 axis stabilised reconnaissance camera has been designed by Prof.Alexender Koh of the Bath Spa University, UK. The camera is fitted on an anti vibration mount and shock absorbers. The restrictive array size (1000×1000 ) of such cameras and low cost make them popular among imagery users with small areas of coverage requirements especially geologists, forestery officials, coast line monitoring organisations.Source:
Fig 2. A GeoTechnologies SF-DMC small format digital mapping camera
Single Lens colour cameras with multiple arrays
These cameras used separate ccd or cmos arrays for near simultaneous acquisition of data. This removes the need of mosaic filters and Bayer interpolation resulting in better colour redention.
Global Imaging Technologies G2010
The GIT G2010 sensor is capable of simultaneously collecting data in RGB as well as NIR by triggering frames within a hundredth of a microsecond of each other. This results in no noticeable registration error. The 12 bit image depth capability though available, studies by Global Imaging Technologies have shown that the added bit depth ( regular 8 bit) contributed little or nothing to the quality for 99% of end users.
Single Lens Cameras with beam splitters
These cameras are exclusively made by Redlake and have an extremely small array (1000×1400 – MS3100 and 1000×1900 – MS4100). The light entering through the lens is separated into individual bands (3) using a dichroic prism resulting in perfect registration of the acquired multiband imagery which is recorded by 3 separate ccd arrays . The data is acquired in 24 bit quantisation in the visible range and 8 bits in the IR range. )
Fig 3.a.GIT G2010 small format camera, b. Principle of a beam splitter.