Image lag optimisation in a 4T CMOS image sensor for the JANUS camera on ESA's JUICE mission to Jupiter

The CIS115, the imager selected for the JANUS camera on ESA’s JUICE mission to Jupiter, is a Four Transistor (4T) CMOS Image Sensor (CIS) fabricated in a 0.18 µm process. 4T CIS (like the CIS115) transfer photo generated charge collected in the pinned photodiode (PPD) to the sense node (SN) through the Transfer Gate (TG). These regions are held at different potentials and charge is transferred from the potential well under PPD to the potential well under the FD through a voltage pulse applied to the TG. Incomplete transfer of this charge can result in image lag, where signal in previous frames can manifest itself in subsequent frames, often appearing as ghosted images in successive readouts. This can seriously affect image quality in scientific instruments and must be minimised. This is important in the JANUS camera, where image quality is essential to help JUICE meet its scientific objectives. This paper presents two techniques to minimise image lag within the CIS115. An analysis of the optimal voltage for the transfer gate voltage is detailed where optimisation of this TG “ON” voltage has shown to minimise image lag in both an engineering model and gamma and proton irradiated devices. Secondly, a new readout method of the CIS115 is described, where following standard image integration, the PPD is biased to the reset voltage level (VRESET) through the transfer gate to empty charge on the PPD and has shown to reduce image lag in the CIS115

Quantitative precipitation forecasting over Narmada catchment

Quantitative precipitation forecasting (QPF) has been attempted over the Narmada Catchment following a statistical approach. The catchment has been divided into five sub-regions for the development of QPF models with a maximum lead-time of 24 hours. For this purpose the data of daily rainfall from 56 raingauge stations, twice daily observations on different surface meteorological parameters from 28 meteorological observatories and upper air data from 11 aerological stations for the nine monsoon seasons of 1972-1980 have been utilized. The horizontal divergence, relative vorticity, vertical velocity and moisture divergence are computed using the kinematic method at different pressure levels and used as independent variables along with the rainfall and surface meteorological parameters. Multiple linear regression equations have been developed using the stepwise procedure separately with actual and square root and log-transformed rainfall using 8-year data (1972-1979). When these equations were verified with an independent data for the monsoon season of 1980, it was found that the transformed rainfall equations fared much better compared to the actual rainfall equations. The performance of the forecasts of QPF model compared to the climatological and persistence forecasts has been assessed by computing the verification scores using the forecasts for the monsoon season of 1980

Decreasing trend in the rainfall of Kerala

The rainfall time series of 75 rain recording stations over Kerala for the 80-year period 1901 to 1980 have been statistically examined for long-term trends. Application of Mann-Kendall rank statistic test to the time series of annual and seasonal totals as well as extreme rainfall of 1, 2, 3...10 day durations revealed a significant decreasing trend in the rainfall over the eastern high lands and adjacent areas to the west. This finding is supported by the fact that the mean rainfall for the second half of the period is 10 to 20% lower than for the first half over the same area

IMPLEMENTATION OF REJECTION STRATEGIES INSIDE MALAYALAM CHARACTER RECOGNITION SYSTEM BASED ON RANDOM FOURIER FEATURES AND REGULARIZED LEAST SQUARE CLASSIFIER

Robust and reliable recognition are indeed necessary requirements for optical character recognition systems. Distortions present in the document image and the pre-processing errors cause the optical character recognition system to apply rejection policies to achieve reliable recognition in computer assisted applications. The objective of this paper is to implement a robust and reliable character recognition system for Malayalam language. Random Fourier features classified with Regularized Least Square loss function based Regression classifier can approximate the non-linear kernel machines. Baseline Malayalam character recognition based on Random Fourier features and Regularized Least Square regression classifier is implemented in this paper. Up on this baseline character recognition system, rejection strategies are applied and are experimented with real world document images. An improvement in recognition accuracy is achieved with the simulated Malayalam character recognition system at the cost of rejecting character images having low classification score

Soft X-ray radiation damage in EM-CCDs used for Resonant Inelastic X-ray Scattering

Advancement in synchrotron and free electron laser facilities means that X-ray beams with higher intensity than ever before are being created. The high brilliance of the X-ray beam, as well as the ability to use a range of X-ray energies, means that they can be used in a wide range of applications. One such application is Resonant Inelastic X-ray Scattering (RIXS). RIXS uses the intense and tuneable X-ray beams in order to investigate the electronic structure of materials. The photons are focused onto a sample material and the scattered X-ray beam is diffracted off a high resolution grating to disperse the X-ray energies onto a position sensitive detector. Whilst several factors affect the total system energy resolution, the performance of RIXS experiments can be limited by the spatial resolution of the detector used. Electron-Multiplying CCDs (EM-CCDs) at high gain in combination with centroiding of the photon charge cloud across several detector pixels can lead to sub-pixel spatial resolution of 2–3 μm. X-ray radiation can cause damage to CCDs through ionisation damage resulting in increases in dark current and/or a shift in flat band voltage. Understanding the effect of radiation damage on EM-CCDs is important in order to predict lifetime as well as the change in performance over time. Two CCD-97s were taken to PTB at BESSY II and irradiated with large doses of soft X-rays in order to probe the front and back surfaces of the device. The dark current was shown to decay over time with two different exponential components to it. This paper will discuss the use of EM-CCDs for readout of RIXS spectrometers, and limitations on spatial resolution, together with any limitations on instrument use which may arise from X-ray-induced radiation damage

Non-linear responsivity characterisation of a CMOS Active Pixel Sensor for high resolution imaging of the Jovian system

The Jovian system is the subject of study for the Jupiter Icy Moon Explorer (JUICE), an ESA mission which is planned to launch in 2022. The scientific payload is designed for both characterisation of the magnetosphere and radiation environment local to the spacecraft, as well as remote characterisation of Jupiter and its satellites. A key instrument on JUICE is the high resolution and wide angle camera, JANUS, whose main science goals include detailed characterisation and study phases of three of the Galilean satellites, Ganymede, Callisto and Europa, as well as studies of other moons, the ring system, and irregular satellites. The CIS115 is a CMOS Active Pixel Sensor from e2v technologies selected for the JANUS camera. It is fabricated using 0.18 μm CMOS imaging sensor process, with an imaging area of 2000 × 1504 pixels, each 7 μm square. A 4T pixel architecture allows for efficient correlated double sampling, improving the readout noise to better than 8 electrons rms, whilst the sensor is operated in a rolling shutter mode, sampling at up to 10 Mpixel/s at each of the four parallel outputs.A primary parameter to characterise for an imaging device is the relationship that converts the sensor's voltage output back to the corresponding number of electrons that were detected in a pixel, known as the Charge to Voltage Factor (CVF). In modern CMOS sensors with small feature sizes, the CVF is known to be non-linear with signal level, therefore a signal-dependent measurement of the CIS115's CVF has been undertaken and is presented here. The CVF is well modelled as a quadratic function leading to a measurement of the maximum charge handling capacity of the CIS115 to be 3.4 × 104 electrons. If the CIS115's response is assumed linear, its CVF is 21.1 electrons per mV (1/47.5 μV per electron)