Image Formation Time Research Articles

Incoherent Imaging at Microwave and Millimeter-Wave Frequencies Using Noise Transmitters

We present recent results of a new form of microwave and millimeter-wave imaging called active incoherent millimeter-wave (AIM) imaging that combines noise radar and sparse interferometric imaging techniques. Illumination of the scene with spatially and temporally incoherent noise enables the use of a sparse receiving array to capture information in the spatial frequency domain and reconstruct the scene intensity via Fourier transform. Whereas current passive interferometric imaging systems require high-gain receivers and long integration times, the use of active illumination enables image formation with comparatively low-gain receivers and fast enough image formation time to support real-time imaging. Compared to traditional active imaging systems, no beam scanning is necessary, simplifying the system architecture and providing a staring architecture. We review the fundamental theory behind AIM imaging and present results of three recent experimental implementations at microwave and millimeter-wave frequencies.

Improved Method of Video Synthetic Aperture Radar Imaging Algorithm

Video synthetic aperture radar (ViSAR) is a novel imaging model to persistently surveil the region of interest by a series of consecutive images in real time. The formation time of one frame image, which can influence the image latency, is one of the key factors to realize ViSAR system. In general, the polar format algorithm (PFA) is preferred for ViSAR imaging. However, the 2-D resampling in the PFA has a large computation burden and is complex to realize in the real-time processing system. It has become the main obstacle to reduce image latency. Therefore, we derive four judgment criteria in this letter. According to these criteria, we propose the improved method of the PFA. Based on this method, the modified PFA can reduce the image formation time while guaranteeing the image quality. Simulation results are presented to validate the effectiveness of the improved method proposed in this letter.

An Adaptive Fast Factorized Back-Projection Algorithm With Integrated Target Detection Technique for High-Resolution and High-Squint Spotlight SAR Imagery

This paper deals with the problem of fast focusing the spotlight synthetic aperture radar (SAR) data in high-resolution and high-squint mode, which has shown its potential capacity in various military SAR applications. Fast factorized backprojection (FFBP) is considered as an ideal methodology for high-resolution and high-squint SAR imagery. However, FFBP performs pixel-by-pixel interpolation, yielding heavy computational burden and limiting its real-time processing. In this paper, target detection technique, which is used as a discrimination tool to retain the target pixels and reject the clutter and noise pixels, is integrated into the subaperture imaging chain during FFBP implementation, aiming to speed up the overall image formation time. Due to the characteristic of spotlight acquisition, an adaptive processing scheme is developed for multiple subaperture images detection. With the integrated target detection technique, only the target pixels need to be interpolated and accumulated coherently. Without loss of focusing performance, the number of interpolations is dramatically reduced. The proposed fast imaging algorithm is named as adaptive FFBP (AFFBP), and it has distinctive superiority for sparse scene reconstruction, such as the maritime target imaging. AFFBP has been successfully applied to two simulated scenes with high and low signal-to-noise ratios (SNRs), and two real measured datasets with squint angle high up to $50^{\circ }$ and $70^{\circ }$ , respectively. All these experiments demonstrate the effectiveness and efficiency improvement of the proposed AFFBP algorithm.

The Importance of Image Formation Time in Image-Aided Methods for Word Memorization

The present study investigated whether the length of time subjects are allowed for image formation in image-aided word-memorization protocols influences recall. To this end, we selected 363 high-school students who were presented with a list of 24 words to be learned by the rote method, an image-aided method with normal image, or an image-aided method with bizarre image; the time allowed for image formation was 10, 20, or 40 seconds. Recall was then evaluated immediately after the test and 1 day later. Each subject participated in only 1 experimental condition. Our results indicate that both immediate and delayed free recall were significantly better in the image-aided groups than in the rote groups. Considering the image-aided groups, both immediate and delayed recall were affected by image type used and image presentation time, with recall significantly better in the 40-second group than in the other 2 groups. Significant differences were also detected between the image types.

Thermographic system with a laser scanning device

It is shown that laser photothermal radiometry (LPTR) in combination with laser beam scanning within the instantaneous field of view of a single-element photodetector can be used to develop a scanning thermal emission microscope. An expression is derived for estimating its temperature resolution. The results of calculations are presented and the factors influencing the spatial lateral resolution of the technique and the time of image formation with the help of an acousto-optical deflector are analysed.

Enhancing Fire Scar Anomalies in AVHRR NDVI Time‐Series Data

Fire mapping science can benefit from standard techniques for analyzing time‐series data. The Z transform produces the z‐score, termed a standardized variable because the units are dimensionless standard deviations. The Z transform represents a simple, older way to characterize non‐image data, but is presented here as a new way to enhance fire scar anomalies in image time‐series data. The transform is invertible, and can be applied to any continuous, gridded data. Time series data from the Advanced Very High Resolution Radiometer (AVHRR) are featured. When applied in the x, y (i.e., spatial) plane of AVHRR Normalized Difference Vegetation Index (NDVI) data, the Z transform places each NDVI value in the statistical context at the time of image formation, producing Z‐standardized NDVI (ZNDVI) values. Invoking the Z transform across the z (time series) plane of ZNDVI images produces a multitemporal Z (MTZ) score for each pixel in a ZNDVI target image for a selected time step. The MTZ image thus depicts the deviation or departure of a given pixel, for a specific step in the series, relative to the mean for that pixel across the time series. A case study demonstrates an MTZ enhancement of AVHRR NDVI data that enhances in the Rincon Mountains east of Tucson, Arizona unusually low NDVI values associated with a 1994 wildfire scar. Enhancements are confirmed using higher‐resolution remote sensor data from the Landsat Thematic Mapper (TM).

Finite element analysis of SCALPEL wafer heating

A high-throughput scattering with angular limitation projection electron beam lithography (SCALPEL) tool will typically deliver up to 1.5×10−4 J to an area of 250 μm×250 μm over a time of 200 μs, corresponding to a power input of 0.75 W. This heat deposition occurs in the upper 60 μm of a wafer creating local thermal strain at the time of image formation, and depends on mask and tool conditions and specific boundary conditions. Initial modeling results indicate expansion-induced peak pattern placement errors of ∼1 nm on a local scale (i.e., a 3 mm effective field size), several nanometers in a chip area, and a few microns overall. Since the use of a mainly predictive correction algorithm is anticipated, it is vital to conduct a rigorous investigation of the heat transfer and strain formation. Results are presented of such an analysis, illustrating the heating response for the fundamental building blocks of the SCALPEL writing strategy.

Initial wafer heating analysis for a SCALPEL lithography system

A high-throughput SCALPEL tool will employ a typical exposure current of 30 μA and electron column potential of 100 KV, delivering power up to ∼3 W through a 0.25 mm (wafer scale) square optical sub-field. Electrons lose energy to form heat in the upper 60 μm of a wafer in vacuum during a sub-field exposure period of ∼200 microseconds, creating significant local wafer heating at the time of image formation. Our initial analysis indicates that expansion-induced pattern placement errors will require a sub-field position correction strategy.

Image-Formation Time is Not Related to Recall of Bizarre and Plausible Images

Past studies of bizarre imagery in which image-formation time is reported have not directly investigated the potential relation of that measure to recall. In the present study, 50 subjects spontaneously formed images from pairs of words to test the idea that quickly formed images are recalled more often. There was no relationship between image-formation time and recall. Image bizarreness and image interaction did not facilitate recall, and there were no differences in the times required to form bizarre and plausible images. The latter findings, which are inconsistent with much of the past research, may be the result of allowing subjects to form images spontaneously, rather than specifying the image to be formed.

Photoelectroplating Light Modulator

A two-dimensional light modulator has been developed based on the principle of photon controlled electroplating of metal onto a photoconducting semiconductor. It may be used in transmission or reflection, and forms positive or negative images. Some observed characteristics of the modulator are: 18-line pairs/mm resolution, reusability to the extent of about ten cycles, and image formation time of 0.5-5 sec. Other experimental observations are described, and device performance is analyzed in terms of semiconductor parameters.