Hanying Zhou

Technology development towards WFIRST-AFTA coronagraph

NASA’s WFIRST-AFTA mission concept includes the first high-contrast stellar coronagraph in space. This coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. In this paper we present the plan for maturing coronagraph technology to TRL5 in 2014-2016, and the results achieved in the first 6 months of the technology development work. The specific areas that are discussed include coronagraph testbed demonstrations in static and simulated dynamic environment, design and fabrication of occulting masks and apodizers used for starlight suppression, low-order wavefront sensing and control subsystem, deformable mirrors, ultra-low-noise spectrograph detector, and data post-processing.

Automatic target recognition field demonstration using a grayscale optical correlator

Jet Propulsion Laboratory (JPL) has recently developed a camcorder-sized grayscale optical correlator (GOC) for real- time automatic target recognition applications. Key features of this GOC include: a grayscale input SLM to accommodate direct interface with the input imaging sensor, a real-valued (bipolar-amplitude) filter spatial light modulator to enable use of a MACH (Maximum Average Correlation Height) composite correlation filter algorithm, compact and portable. This GOC architecture has greatly improved the system complexity by removing the need of preprocess (binarization) the input, and the powerful MACH composite filter has greatly reduced the number of filter templates. Updating of the GOC system will be described in this paper, a recent real-time field demonstration for target recognition and tracking at Mojave Desert, CA will also be reported.

Neural network post-processing of grayscale optical correlator

In real-world pattern recognition applications, multiple correlation filters can be synthesized to recognize broad variation of object classes, viewing angles, scale changes, and background clutters. Composite filters are used to reduce the number of filters needed for a particular target recognition task. Conventionally, the correlation peak is thresholded to determine if a target is present. Due to the complexity of the objects and the unpredictability of the environment, false positive or false negative identification often occur. In this paper we present the use of a radial basis function neural network (RBFNN) as a post-processor to assist the optical correlator to identify the objects and to reject false alarms. Image plane features near the correlation peaks are extracted and fed to the neural network for analysis. The approach is capable of handling large number of object variations and filter sets. Preliminary experimental results are presented and the performance is analyzed.

Development of streamlined OT-MACH-based ATR algorithm for grayscale optical correlator

JPL is developing an Advanced Autonomous Target Recognition (AATR) technology to significantly reduce broad area search workload for imagery analysts. One of the algorithms to be delivered, as part of JPL ATR Development and Evaluation (JADE) project, is the OT-MACH based ATR algorithm software package for grayscale optical correlator. In this paper we describe the basic features and functions of the software package as currently implemented. Automation of filter synthesis and test for GOC, particularly the automation of OT-MACH parameter optimization, is discussed.

Compact Holographic Data Storage System

JPL, under current sponsorships from NASA Space Science and Earth Science Programs, is developing a high-density, nonvolatile and rad-hard advanced Compact Holographic Data Storage (CHDS) system to enable large-capacity, high-speed, low power consumption, and read/write of data for potential commercial and NASA space applications. This CHDS system consists of laser diodes, photorefractive crystal, spatial light modulator, photodetector array, and I/O electronic interface. In operation, pages of information would be recorded and retrieved with random access and high-speed. The non-volatile, rad-hard characteristics of the holographic memory will provide a revolutionary memory technology to enhance mission capabilities for all NASAs Earth Science Mission.

Low-CNR inverse synthetic aperture LADAR imaging demonstration with atmospheric turbulence

An Inverse Synthetic Aperture LADAR (ISAL) system is capable of providing high resolution surface mapping of near Earth objects which is an ability that has gained significant interest for both exploration and hazard assessment. The use of an ISAL system over these long distances often presents the need to operate the optical system in photon-starved conditions. This leads to a necessity to understand the implications of photon and detector noise in the system. Here a Carrier-to-Noise Ratio is derived which is similar to other optical imaging CNR definitions. The CNR value is compared to the quality of experimentally captured images recovered using the Phase Gradient Autofocus technique both with and without the presence of atmospheric turbulence. A minimum return signal CNR for the PGA to work is observed.

512x512 high-speed grayscale optical correlator

Jet Propulsion Laboratory has developed a new 512 X 512 high-speed grayscale optical correlator (GOC) for real-time automatic target recognition (ATR) applications. As compared with a previous developed 128 X 128 grayscale optical correlator, the utilization of a pair of high-resolution input spatial light modulator (SLM) has increased the input field of view by 16 times. The use of a matching high- resolution filter SLM has increased the sharpness of the correlation peak. Key features of this GOC include: a grayscale input SLM (Kopin 640 X 480, 8-bit) to accommodate direct interface with the input imaging sensor. A real-valued (bipolar-amplitude) filter SLM (512 X 512, 4-bit) to enable use of a MACH (Maximum Average Correlation Height) composite correlation filter algorithm, compact and portable. This GOC architecture has greatly improve the system complexity by removing the need of preprocessing (binarization) the input, and the powerful MACH composite filter has greatly reduced the number of filter templates. In this paper, the criterion of selection of both input and filter SLM will be discussed. System analysis of building a compact correlator will also be provided. Experimental ATR verification of the 512 X 512 GOC will also be illustrated.

Grayscale optical correlator for real-time onboard ATR

Jet Propulsion Laboratory has been developing grayscale optical correlator (GOC) for a variety of automatic target recognition (ATR) applications. As reported in previous papers, a 128 X 128 camcorder-sized GOC has been demonstrated for real-time field ATR demos. In this paper, we will report the recent development of a prototype 512 X 512 GOC utilizing a new miniature ferroelectric liquid crystal spatial light modulator with a 7-micrometers pixel pitch. Experimental demonstration of ATR applications using this new GOC will be presented. The potential of developing a matchbox-sized GOC will also be discussed. A new application of synthesizing new complex-valued correlation filters using this real-axis 512 X 512 SLM will also be included.

Low-cost chirp linearization for long-range ISAL imaging application

High quality linear laser frequency chirp of high chirp rate is critical to many laser ranging applications. In this paper, we describe a cost-effective chirp linearization approach implemented on our Inverse synthetic Aperture LADAR (ISAL) imaging testbed. Our approach uses a COTS PZT for external cavity laser frequency tuning and a common self-heterodyne fiber interferometer as a frequency monitor, with a two-step hardware and software chirp linearization procedure to achieve high quality chirp. First, the nominal triangle waveform input to PZT drive is modified through an iterative process prior to ISAL imaging acquisition. Several waveforms with chirp rates between 1 and 4THz/s have been acquired with residual chirp rate error ~ +/-2% in usable region. This process generally needs to be done only once for a typical PZT that has excellent repeatability but poor linearity. The modified waveform is then used during ISAL imaging acquisition without active control while the imperfection in transmitted frequency is monitored. The received imaging data is resampled digitally based on frequency error calculated from the frequency monitor data, effectively reduce chirp nonlinearity to ~+/- 0.2% in chirp rate error. The measured system impulse response from return signal shows near designed range resolution of a few mm, demonstrating the effectiveness of this approach.

Laboratory Performance of the Shaped Pupil Coronagraphic Architecture for the WFIRST-AFTA Coronagraph

One of the two primary architectures being tested for the WFIRST-AFTA coronagraph instrument is the shaped pupil coronagraph, which uses a binary aperture in a pupil plane to create localized regions of high contrast in a subsequent focal plane. The aperture shapes are determined by optimization, and can be designed to work in the presence of secondary obscurations and spiders - an important consideration for coronagraphy with WFIRST-AFTA. We present the current performance of the shaped pupil testbed, including the results of AFTA Milestone 2, in which ≈ 6 × 10-9 contrast was achieved in three independent runs starting from a neutral setting.