The Wideband Arecibo Pulsar Processor - SNAP Page

WAPP- SNAP (Snapshoot) Program

Introduction

SNAP is an application that can process raw WAPP files. It is not intended to be a full data reduction package, instead it can be used for diagnostics and on-line evaluation of data quality.

Data Source Modes

SNAP can receive data from two possible sources. First, it can read WAPP data files and process them off-line. This must be done off-line because accessing WAPP data files during an active observation could easily disturb an observation and cause data acquistion to fail. Therefore, a second mode takes data directly from the WAPP realtime process. This mode communications via sockets with the WAPP progam and has been designed to eliminated any possible problems with contention of WAPP resources during an active observation.

Record Size

Both modes (SNAP and WAPP) process data in blocks of 2048 records. Each record represents the data taken during a single time segement. Thus, a record could have 1,2 or 4 correlations depending on the mode (4 for full stokes)

Header and Control Window

The main SNAP window has several control buttons and a text dump of a WAPP header.

Display Windows

Plot Images

The plot window presents the WAPP data as different types of XY plots. Which plot is presented can be set from the Select menu. The slider is used to select records in several display modes. The Dump Raw button is a diagnositic command to write the raw correlation function (unprocessed) to standard out. A mouse selection function can produce exact values in the parameter boxes.

Raw Band Mode

This is a raw linear plot of the bandpass (Fourier transform of the correlation function). By moving the slider, it is possible to view all 2048 records.

Sig-Ref Mode

A crude bandpass removal. The reference band is computed by simply averaging all 2048 data records. This psuedo-reference is then subtracted from the each raw bandpass.

Ref Band Mode

Display

Freq Bin

Displays all data along one frequency bin. Thus, the X axis is record number (or time), while Y is the power. Which frequency bin is displayed is selected by the slider.

Dedisp

This does a simple dedisperse and fold on the 2048 records that exist in memory. It uses the tempo polynominal values and DM value listed in the header to create a pulse profile. In cases where the

Total Power

A simple total power versus record number plot.

Spect TPow

A fourier transform of the meausred total power.

Integ Pulse

The first scan after

Waterfall Images

The plot window presents the WAPP data as different types of color intesity waterfalls. Intensity is shown as different colors (Blue is maximum, Red is minimum intensity). The vertical axis (X) is frequency, with higher frequencies on top. The horizontal axis is time. The left side represents the first record measured, while the last is on the right. Which data is presented in the waterfall can be set from the Select menu on the top of the waterfall window

Raw/Ref

A raw bandpass plot, which shows the bandpass shape.

Sig-Ref

Performs a crude bandpass removal by subtracting the average of all 2048 records

Sig-Ref All

Essentially the same as Sig-Ref, except the entire 2048 records are compressed to fit onto a single display. This avoids scrolling during observation to see an entire block of data.

Note - The display of waterfall images is VERY CPU intensive. If speed is critical and the Waterfall image is not required, the procesing of WAPP files can be greatly expediated by turning off the waterfall display. To disable the procesing of waterfall displays, click on the button in the "" menu... Note, after disabling the waterfall display, it is possible to re-enable them later.

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This document maintained by wapp@naic.edu.
Material Copyright © 2000 Arecibo Observatory - Cornell University