Prepared for
Contract NAS 5-27295
Task Assignment 401

Prepared by: B. E. Turnrose and R. W. Thompson
Reviewd by: D. F. Stone and P. M. Perry
Date: December 20, 1984


This document presents information needed by users of the International Ultraviolet Explorer (IUE) to understand the methods and products of the new reduction software (introduced in November 1980 for low dispersion and November 1981 for high dispersion) of the IUE Spectral Image Processing System (IUESIPS) at GSFC. Although this Version 2.0 reflects the post-November 1981 state of IUESIPS and therefore describes the net effect of the many other changes made to the system since early 1980 when Version 1.0 was issued, its principal purpose is to document the new reduction software. As a result, Version 2.0 complements, but does not supersede, Version 1.0 or its reissue, Version 1.1.


Section 1 - Introduction and Overview

1.1 Purpose of Document
1.2 Philosophy and Scope of IUE Image Processing
1.3 Data Products Summary
1.4 Guest Observer's Image Processing Specifications

Section 2 - Nature of IUE Data

2.1 Image and Label Parameters
2.2 Spectrograph Geometry
2.3 Resolution
2.3.1 High Dispersion (Echelle) mode Resolution Dispersion Direction Resolution Perpendicular to Dispersion Direction
2.3.2 Low Dispersion Mode Resolution in Dispersion Direction Resolution Perpendicular to Dispersion Direction

Section 3 - Raw-Image Screening Operations

3.1 Microphonic Noise Detection
3.2 Bright-Spot Detection
3.3 Partial-Read Image Preprocessing

Section 4 - Geometric Distortion

4.1 Overview
4.2 Reseau Marks (Fiducial Grid)
4.2.1 Measurement of Reseau Positions
4.2.2 Averaging of Reseau Positions
4.3 Parameterization of, and Compensation for, Distortion
4.3.1 Temperature-Dependence Correlations
4.3.2 Temperature-Effect Parameterization for Production Processing Operational Cameras LWR SWP LWP SWR Documentation in Image Labels
4.3.3 Distortion Compensation in Production Processing Goem-to-Raw Mapping Function G-1 Raw-to-Geom Mapping Function G

Section 5 - Photometric Correction

5.1 Overview
5.2 Intensity Transfer Functions (ITF)
5.2.1 Definition of ITF
5.2.2 Characteristics of ITF ITF Exposure Values and Scale Factors Highest Valid ITF DN Levels
5.3 Conversion of DN to FN
5.3.1 Spatial Mapping and Interpolation
5.3.2 Assignment of Flux Values Normal Interpolation Technique Extrapolation Techniques Negative FN Positive FN Saturated Pixels
5.3.3 Coding of Flux Values in Photometrically Corrected Image File
5.4 Limitations to Photometric Linearity

Section 6 - Wavelength Calibration

6.1 Platinum-Neon Lamp Calibration Images
6.2 Calculation of Dispersion Relations
6.2.1 Dispersion Relation Calculation for Individual Calibration Images
6.2.2 Calculation of Mean Dispersion Constants
6.2.3 Large Aperture Dispersion Relations
6.3 Pre-Extraction Corrections to Dispersion Relations
6.3.1 Temperature and Time Corrections
6.3.2 Registration of Spectral Format Automatic Registration Manual Registration Accuracy
6.4 Post-Extraction Corrections to Wavelengths
6.4.1 Velocity Corrections
6.4.2 Vacuum-To-Air Correction
6.5 Overall Wavelength Accuracy
6.6 Special Calibrations

Section 7 - Extraction of Spectral Flux

7.1 High Dispersion
7.1.1 Point-Source and Extended Source Reduction Modes
7.1.2 Extraction Method Extraction of Gross Flux Extraction and Processing of Background Flux
7.1.3 Computation and Processing of Net Spectral Fluxes Noise-Conditioning Filter Echelle Blaze ("Ripple") Correction
7.1.4 Wavelength Corrections Applied to Extracted Fluxes
7.1.5 Units of Extracted Spectra and Absolute Flux Scaling of Extracted Fluxes Absolute Calibration
7.2 Low Dispersion
7.2.1 Point-Source and Extended-Source Reduction Modes
7.2.2 Extraction Method Spatially Resolved (Line-by-Line) Spectra Slit Integrated Spectra
7.2.3 Wavelength Correction Applied to Extracted Fluxes
7.2.4 Units of Extracted Spectra and Absolute flux Calibration Scaling of Extracted Fluxes Absolute Calibration
7.3 Data Quality Flag (Epsilon) Values

Section 8 - Guest Observer Data Package

8.1 Output Products Description
8.1.1 Photowrite Hardcopy Images Processed Data Raw Data Photometeric Considerations
8.1.2 CalComp Plots Scaling of Plots Low Dispersion Plots High Dispersion Plots Plot Accuracy and Registration
8.1.3 Magnetic Tapes Low Dispersion Files High Dispersion Files Other Files
8.1.4 Computer Listings Label Displays Tape Contents Summary
8.2 Magnetic Tape File Formats
8.2.1 Label Records Normal Labels
8.2.2 Data Records Image Files Raw Photometrically Corrected Images Extracted-Spectra Files Other Files Fine Error Sensor (FES) Images Reseau-Position Data Sets

Section 9 - Image Label Contents

9.1 Image Label Overview
9.2 Raw-Image Labels
9.3 Processing-History Portion of Labels
9.3.1 Low Dispersion
9.3.2 High Dispersion
9.4 Non-Standard Labels
9.4.1 Tape Header File
9.4.2 Reseau-Position File
9.5 Label Errors and Modifications

Section 10 - Image Processing System Modifications



1-1IUESIPS Functional Overview
2-1 Schematic Representation of the Echelle (High Dispersion) Spectral Format in the Long Wavelength Prime (LWP) Camera, Small Aperture
2-2 (as above for) `Large Aperture'
2-3 Schematic Representation of the Low Dispersion Spectral Format in the camera, both Apertures
2-4 (as in 2-1 for) `short wavelength Prime (SWP)'
2-5 (as above for) `Large Aperture'
2-6 (as in 2-3 for) `SWP'
2-7 (as in 2-1 for) `Long Wavelength Redundant (LWR)'
2-8 (as above for) 'Large Aperture'
2-9 (as in 2-3 for) `LWR'
2-10 SWP Geometry
2-11 LWP Geometry
2-12 LWR Geometry
4-1 Displacements of Mean Reseaux from Correct Grid, SWP (magnified by 2)
4-2 Displacements of Mean Reseaux from Correct Grid, LWR (magnified by 2)
4-3 Displacements of Mean Reseaux from Correct Grid, LWP (magnified by 2)
4-4a Scatter in the two orthoganal directions (along and perpendicular to high dispersion orders) for the reseau location as observed on 18 SWP flat-field images The length of the bars represents 1s.
4-4b As in Figure 4-4a, but after applying temperature corrections
4-5 Displacements of Mean Reseaux from Correct Grid, LWP (Magnified by 2)
7-1 Adjacent Extraction Slits for Obtaining the Gross Flux (after Lindler, 1982).
7-2 Background Pixel Positions (after Lindler, 1982).
7-3 Bilinear Interpolation for Obtaining Low Dispersion flux values at the position `x'.
7-4 W angles for LWP, LWR and SWP cameras (from Bohlin, Lindler, and Turnrose, 1981)
7-5 Section of Spatially Resolved Extracted Spectrum
7-6 Extraction of Gross and Background Spectra from Spatially Resolved File (from Lindler, 1979).
8-1 Photowrite System Response Function
8-2 Tape Contents Summary Sheet (Last Page of Labelprint Listing)
8-3 Schematic GO Tape Structure
8-4 Standard IUESIPS Label Record Structure
8-5 Data Record Structures (RI and PI)
8-6 Data Record Structure for Spatially Resolved Low Dispersion Spectrum (LBLS).
8-7 Data Record Structure for Merged Low Dispersion Spectra (MELO).
8-8 Data Record Structure for Merged High Dispersion spectra (MEHI).
8-9 Data Record Structures (FES)
8-10 Data Record Structures (RES)
9-1a Labelprint Listing for Raw Image (RI) File (Part 1)
9-1b Labelprint Listing for Raw Image (RI) File (Part 2)
9-2 Labelprint Listing for Merged Low Dispersion Extracted Spectra (MELO) File.
9-3 Labelprint Listing for Merged High Dispersion Extracted Spectra (MEHI) File.
9-4 Labelprint Listing for Tape Header File
9-5 Labelprint Listing of Reseau-Position File


2-1 Official Adopted Dimensions for the Large Apertures in Each Spectrograph, Measured on SWP and LWR Images
2-2 Additional Spectrograph Dimensions of Interest, measured on SWP and LWR Images (Panek, 1982)
2-3 Standard Offsets from the small to the large Spectrograph Aperture, used by IUESIPS since 6 August 1979 (in pixel units)
2-4 Approximate Spectral Scales in Each Dispersion Mode
3-1 Hot Pixels in the SWP Camera
3-2 Hot Pixels in the LWR Camera
3-3 Standard Partial-Read Parameters
4-1 Mean SWP Reseau Displacement Values
4-2 Mean LWR Reseau Displacement Values
4-3 Mean LWP Reseau Displacement Values
4-4 R1 Constants for SWP Displacement Correction
4-5 R2 THDA Coefficients for SWP Displacement Correction
5-1 Approximate Highest DN Values in the ITF
5-2 Effective Exposure Times in ITF's
5-3 Scale Factors for ITF's
5-4 Center and Radius Values Defining Region of Photometric Correction
5-5 Coding of Pixel FN Values in the PI File
6-1 Coefficients defining the dispersion relations for the small aperture
6-2 Error (16 in pixels) for various corrections to the mean dispersion constants
6-3 Search Area Wavelengths
7-1 Optimal Weights Currently Used for Filtering High Dispersion Net Spectra
7-2 Echelle Ripple Parameters
7-3 Original and May 1980 Calibrations for LWR
7-4 Original and May 1980 Calibrations for SWP
7-5 Data Quality Flag (Epsilon) Values
8-1 Explanatory Key to Figure 8-2
8-2 Format of Scale Factor Record (Record Sequence Number Zero)
9-1 Key to Figure 9-1
9-2 Key to Figure 9-2
9-3 Key to Figure 9-3
18 Dec 1997