Defence Research Agency

About: Defence Research Agency is a based out in . It is known for research contribution in the topics: Synthetic aperture radar & Radar. The organization has 1211 authors who have published 1109 publications receiving 31542 citations.

Texture segmentation and region classification by orthogonal decomposition of co-occurrence matrices

Abstract: Techniques are presented for determining the periodicity and scale of texture; this information is used to define an adaptive transform based on edge co-occurrence matrices for segmenting textured regions. The texture of the region is characterised by an orthogonal decomposition of the co-occurrence matrix using 2-dimensional discrete Hermite functions. The coefficients of this decomposition provide a low order feature vector which can be used for texture classification. >

Balancing optical path lengths in broadband fiber interferometers.

Abstract: A simple model is used to show that control of dispersion in an all-fiber stellar interferometer is feasible. From the results we assume that an interferometer control system is available in which both temperature and strain are used to balance the interferometer. Within the restriction of a single polarization mode, it is shown that vacuum path errors before the coupling of starlight into the fibers as well as fiber-length differences and environmental differences between two fibers can be corrected to high order.

Gas Turbine Exhaust Emissions Monitoring Using Nonintrusive Infrared Spectroscopy

Abstract: Infrared (IR) spectra of the exhaust emissions from a static gas turbine engine have been studied using Fourier Transform (FT) spectroscopic techniques. Passive detection of the infrared emission from remote (range {approximately}3 m) hot exhaust gases was obtained nonintrusively using a high spectral resolution (0.25 cm{sup {minus}1}) FTIR spectrometer. Remote gas temperatures were determined from their emission spectra using the total radiant flux method or by analysis of rotational line structure. The HITRAN database of atmospheric species was used to model the emission from gas mixtures at the relevant temperatures. The spatial distribution of molecular species across a section transverse to the exhaust plume {approximately}10 cm downstream of the jet pipe nozzle was studied using a tomographic reconstruction procedure. Spectra of the infrared emission from the plume were taken along a number of transverse lines of sight from the centerline of the engine outwards. A mathematical matrix inversion technique was applied to reconstruct the molecular concentrations of CO and CO{sub 2} in concentric regions about the centerline. Quantitative measurement of the molecular species concentrations determined nonintrusively were compared with results from conventional extractive sampling techniques.

Diving Responses in Experienced Rebreather Divers: Short-Term Heart Rate Variability in Cold Water Diving

Abstract: Introduction Technical diving is very popular in Finland throughout the year despite diving conditions being challenging, especially due to arctic water and poor visibility. Cold water, immersion, submersion, hyperoxia, as well as psychological and physiological stress, all have an effect on the autonomic nervous system (ANS). Materials and methods To evaluate divers' ANS responses, short-term (5 min) heart rate variability (HRV) during dives in 2-4°C water was measured. HRV resting values were evaluated from separate measurements before and after the dives. Twenty-six experienced closed circuit rebreather (CCR) divers performed an identical 45-meter decompression dive with a non-physical task requiring concentration at the bottom depth. Results Activity of the ANS branches was evaluated with the parasympathetic (PNS) and sympathetic (SNS) indexes of the Kubios HRV Standard program. Compared to resting values, PNS activity decreased significantly on immersion with face out of water. From immersion, it increased significantly with facial immersion, just before decompression and just before surfacing. Compared to resting values, SNS activity increased significantly on immersion with face out of water. Face in water and submersion measures did not differ from the immersion measure. After these measurements, SNS activity decreased significantly over time. Conclusion Our study indicates that the trigeminocardiac part of the diving reflex causes the strong initial PNS activation at the beginning of the dive but the reaction seems to decrease quickly. After this initial activation, cold seemed to be the most prominent promoter of PNS activity - not pressure. Also, our study showed a concurrent increase in both SNS and PNS branches, which has been associated with an elevated risk for arrhythmia. Therefore, we recommend a short adaptation phase at the beginning of cold-water diving before physical activity.