Make : Keo Scientific,
Model : Sentry 3 Imager
A multi-wavelength photometer with wide field-of-view (~180 o) imaging capabilities enabled by a CCD camera (512x512 or 1024x1024 pixels). The centre wavelengths of filters typically deployed: 630.0 nm, 777.4 nm, 557.7 nm, 589.2 nm, 572.5 nm and wideband between 700 and 930.0
Remote sensing of airglow emissions by means of photometric observations has been rigorously pursued by IIG scientists for more than two decades. Photometers utilize multiple interference filters and those measuring the line intensities of rotational-vibrational band of OH emission emanating from ~87 km can yield a measure of rotational temperatures (equivalent to kinetic temperatures at those heights). All-sky imagers are wide field-of-view photometers that can yield useful information on small-scale gravity waves perturbing the airglow layers.
A multi-step procedure involving (i) determination of field-of-view, (ii) Image Calibration, (iii) Regridding, (iv) Star field removal, (v) Background and flat field correction and finally (vi) time differencing
An example of a gravity wave event detected from Tirunelveli: Time difference images of wave event observed on the night of February 14/15. a) OH image, b) Cross sections from a sequence of images taken along the arrow shown in OH image at the mentioned times. The slanting lines represent the motion of crests to the left as time progress, c) Na image, d) OI image. (the axes show distances in km).