http://nopr.niscair.res.in/handle/123456789/3779 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/4716 Title: Wind profiler radar for understanding the tropical convective boundary layer during different seasons <br/> <br/>Authors: Reddy, K Krishna; Kozu, Toshiaki; Rao, D Narayana <br/> <br/>Abstract: <smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place" downloadurl="http://www.5iantlavalamp.com/"> This paper elucidates tropical continental boundary layer structures and their evolutions during different seasons over Gadanki, Southern India. Gadanki-LAWP (Lower Atmospheric Wind Profiler Radar) has proved to be an excellent tool for studying convective structures and boundary layer depth with good temporal (~ 10 min) and vertical resolution (150 m). We used LAWP reflectivity, Doppler velocity and spectral width data in time versus altitude to characterize general behaviour of convective boundary layer based on the “morning” and “evening” transition. From a wide variety of observed patterns, three categories are identified: (i) Descent, (ii) Ascent, and (iii) Inversion Layer (IL). Long-term Gadanki-LAWP observational results show the Ascent cases occur on relatively warm and moist days with strong turbulence and weak capping inversion [maximum occurrence in monsoon], descent days occur [pre-monsoon] on warm dry convection days and IL days occur [winter] on dew/fog and drier days with subsidence inversion and/or advection of warm air from the Bay of Bengal. </smarttagtype> <br/> <br/>Page(s): 105-115 http://nopr.niscair.res.in/handle/123456789/4715 Title: Radiometric scene correction of temporal multi-spectral satellite data for crop discrimination <br/> <br/>Authors: Sahoo, R N; Tomar, R K; Rao, C S; Sehgal, V K; Charchi, Nirupa; Abrol, I P; Tiwari, M K; Wadhawani, M K <br/> <br/>Abstract: Multi-date satellite images under different conditions of the same area are difficult to compare because of change in atmospheric propagation, sensor response and illuminations. To overcome this problem, a radiometric normalization technique, which is based on the statistical invariance of the reflectance of man-made in-scene elements (pseudo invariant features) was attempted. The LISS-III data of IRS-1D of three dates were taken for discrimination of crops and retrieval of crop statistics. To develop temporal NDVI profile of the various crop types, relative image-to-image radiometric scene normalization of each band was done using linear transformation. Water body, orchard and other less dynamic features were excluded and multidate-NDVI image having only agricultural crops was obtained for identification and classification of various crops. Nine classes were identified and discriminated as different crops by analyzing temporal NDVI profile pattern based on ground truth, crop calendar and information on crop sowing and harvesting time. Spatial distribution of different crops was analyzed and crop area statistics was computed. <br/> <br/>Page(s): 116-121 http://nopr.niscair.res.in/handle/123456789/3837 Title: Theoretical analysis on circular sector microstrip antennas <br/> <br/>Authors: Tiwari, V K; Kimothi, Aradhana; Bhatnagar, D; Saini, J S; Saxena, V K; Kumar, P <br/> <br/>Abstract: A rigorous theoretical analysis of a circular sector microstrip antenna with sector angle ⍺ is carried out. General expressions for radiated fields by antenna are derived by applying cavity model based modal expansion technique and are used to study its radiation parameters. Similar to a circular disk antenna, better results for circular sector antenna are also obtained in TM11 mode of excitation. The computed results of a sector antenna with ⍺ = 60º are compared with simulation results and a difference of 2.5%, 38%, 7% and 1.9%, respectively in resonance frequency; input impedance, directivity and bandwidth is recorded. <br/> <br/>Page(s): 133-138 http://nopr.niscair.res.in/handle/123456789/3836 Title: RF loss profile measurement for a high gain, broadband helix TWT <br/> <br/>Authors: Kumar, Vikas; Vohra, Anil; Srivastava, Vishnu <br/> <br/>Abstract: Helix type structure is widely used as slow wave structure in the travelling wave tube (TWT) due to its natural wide bandwidth. Reflections present in the structure may cause oscillations and hence instability in the device. In order to minimize the reflections, a coating of lossy material is done on the helix support rods in a TWT. The loss introduced by such coating has significant effects on the characteristics of the device. In the conventional methods the loss due to this coating (also known as the loss profiles) can be measured only on a single rod before fabrication of the slow wave structure (SWS) assembly. In the present work a new and convenient method has been developed for the measurement of loss profiles of a fabricated SWS assembly. Using the new method an experimental study has been made on a high gain TWT that is made in two sections with sever in between. The loss profiles along the axis of helical SWS have been measured at the sever end. This measurement is found to be very helpful to ensure the accuracy of the final fabricated assembly. <br/> <br/>Page(s): 129-132