Spectrograph Mode OverviewLarry J. PaxtonGUVI co-PISSUSI PI

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.

Spectrograph Mode Data are Continuously being Taken with GUVI

GUVI Spectrographic Mode Produces a full spectrum of 115 – 180 nm FUV Airglow every 3 sec in a fixed direction

SSUSI F19 Checkout Image

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

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.

Interpreting Spectrograph Mode Requires Some Skill

Pick an interesting time…

What is going on in the GUVI data?

Start at L1B Spectrograph Gallery

Picked the orbit on Feb 19 2014 across North America

Look at next day – Feb 20 2014

Feb 21 2014

Feb 21 2014 – next orbit

Feb 21 2014 – next orbit

Quiet time Storm-time

SAA

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

Test Results Using GUVI Spectrograph Data

L1B available since change in mode

Level L1A available back to start of mission

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.

GUVI Spectrograph mode O(135.6) example single orbit data

Example GUVI O/N2 measured in imaging mode prior to scan motor malfunction

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

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

MeV particle noise

Auroral Oval

Equatorial Arcs

Dayglow

Aurora

MeV particle noise

Auroral Oval

Equatorial Arcs

Dayglow

Aurora

2007 Day 135 Orbit 29424

2008 day 127 Orbit 34712

2hrs LST

2008 day 127 Orbit 34712

Development is required to realize those capabilities

NO NASA money for this work We encourage the community to help us

develop new products/capabilities

Spectrograph Mode Data Enable New Capabilities