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Spectrograph Mode Overview. Larry J. Paxton GUVI co-PI SSUSI PI. Spectrograph Mode Data are Continuously being Taken with GUVI. Why spectrograph mode? Spectrograph mode returns the entire spectrum

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spectrograph mode overview

Spectrograph Mode Overview

Larry J. Paxton



spectrograph mode data are continuously being taken with guvi
Spectrograph Mode Data are Continuously being Taken with GUVI
  • Why spectrograph mode?
    • Spectrograph mode returns the entire spectrum
    • When SSUSI was designed the data rate was set as spare words in the OLD data stream – about Flowdown of Requirements is the Same as SSUSI
    • 3816 BITS per second
    • GUVI was similarly constrained by the TIMED project
    • Can only return the entire spectrum when the scan mirror is not in motion due to constraints on the spacecraft NOT the instrument
    • Spectrograph mode gives you insights into the ITM system that are more difficult to achieve in imaging mode in which just “colors” are returned.
GUVI Spectrographic Mode Produces a full spectrum of 115 – 180 nm FUV Airglow every 3 sec in a fixed direction
f19 ssusi detector 2 in spectrograph mode
F19 SSUSI - Detector #2 in Spectrograph Mode
  • Spectrograph mode data were collected using detector #2 and the narrow slit with the scan mirror at nadir.
  • The spectrograph image on the right displays one orbit of data from May 9. The horizontal axis is wavelength. The vertical axis is time. The bright lines on the left side are the 1216Å and 1304Å emissions.
  • Spectrograph image at right shows no evidence of out of band light contamination
interpreting spectrograph mode requires some skill
Interpreting Spectrograph Mode Requires Some Skill
  • GUVI is not fixed in local solar time – it moves through all local times.
  • The spectrograph summary plots provide insight into what is happening
    • Compare from year to year to see if it is driven by “space physics” or “orbital mechanics”
    • Check image plots to see what is visible in a given scene
  • Consult a member of the GUVI team to discuss the details of the operation and the instrument capability.
test results using guvi spectrograph d ata
Test Results Using GUVI Spectrograph Data

Quiet time



O/N2: column density ratio; NO: column density of nitric oxide (100-150 km)

spectrograph mode status
Spectrograph Mode Status
  • The spectrographic mode provides increased effective sensitivity of the instrument.
  • Example data in following slide illustrates data quality.
    • Single wavelength latitudinal plot (OI 135.6)
    • Dayside and aurora brightest features
    • Nightside shows equatorial ionospheric arcs and smaller scale irregularities.
    • The curve labeled “1 sigma noise level” is intended to convey the magnitude of the 1 standard deviation error estimate.
      • It is normally so small that if it had been displayed as “error bars” it would not have been visible.
      • A value at packet number 0 of 20 means that the statistical error in that data point was 20 counts out of about 1500 – for a signal to noise ration of 1500/20 = 75.
o n2 from spectrograph mode fixed mirror confirm data quality
O/N2 from Spectrograph Mode (fixed mirror) confirm data quality
  • A period of elevated geomagnetic activity April 4-7, 2008
  • Observed with GUVI spectrograph mode
  • O/N2 global structure and evolution observed with GUVI
  • confirms spectrograph mode O/N2 data quality.

High Latitude depletions cover all longitudes

spectrograph mode increases our effective sensitivity enormously
Spectrograph mode increases our effective sensitivity enormously
  • The long along track slit means that the effective integration period is now about 9 seconds for a single pixel that is about 5km long (projected to an altitude of 300km)
  • If we sum the data into 50 km “superpixels” then we can bin 10 of these pixels into one superpixel.
  • The effective responsivity is then about 9c/R in each 50 km super pixel.
  • For an effective scale height of 100km for the ionosphere:
    • 1R corresponds to a peak density of about 5x105 cm-3 [5x1011 m-3]
    • 1R corresponds to about 5 TEC units
    • 1 TECU corresponds to about 54 nsec or 16 cm delay in the GPS L1 signal

Auroral Oval



Equatorial Arcs

MeV particle noise


Auroral Oval



Equatorial Arcs

MeV particle noise

spectrograph mode data enable new capabilities
Spectrograph Mode Data Enable New Capabilities
  • Development is required to realize those capabilities
  • NO NASA money for this work
  • We encourage the community to help us develop new products/capabilities