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Dopplergram from Filtergram (FG) Observation. Y. Katsukawa (NAOJ) SOT Team. SOT Dopplergrams (DGs).

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dopplergram from filtergram fg observation

Dopplergram from Filtergram (FG) Observation

Y. Katsukawa (NAOJ)

SOT Team

SOT17 @ NAOJ

sot dopplergrams dgs
SOT Dopplergrams (DGs)
  • Narrowband Filter Imager (NFI) on SOT provides Dopplergrams (DGs) which are images of Doppler (line-of-sight) velocities. Observations with DGs are critically important in studies of photospheric dynamics and helioseismology.
  • The primary photospheric line used for DGs is Fe I 5576 Å which is a line insensitive to the Zeeman effect (Lande g=0).
  • FOV:

80”x160” (1Kx2K) for no summing

320”x160” (2Kx1K) for 2x2 summing

  • 4 uniform wavelength samplings are a standard observable. It takes about 12 secs to make one Dopplergram. 1  30m/s for 2x2 summ.
  • Two wavelength sampling is also available when higher temporal resolution is required.

SOT17 @ NAOJ

5576a 4 wavelengths dopplergrams
5576A 4-wavelengths Dopplergrams
  • The nominal wavelength sampling for 5576A

F1: -90mA, F2: -30mA, F3: +30mA, F4: +90mA

Up to  3km/s velocities are detectable by this sampling.

  • The velocity index R is calculated using the 4 images
  • In order to reduce the telemetry amount, the denominator and the numerator are calculated on-board, and sent to the ground.

Denominator: F1-F2-F3+F4

Numerator: F1+F2-F3-F4

DG obtained at Palo Alto in April, 2005

SOT17 @ NAOJ

5576a 4 wavelengths dopplergrams1
5576A 4-wavelengths Dopplergrams
  • Fe I 5576A spectrum and the transmission profiles of TF at 4 wavelength positions.
  • The relation between the actual Doppler velocities V and the velocity indexes R are calculated using the ideal TF profiles and the atlas spectrum.
  • The Doppler velocities are derived from the velocity indexes R using LUT.

QS

Umbra

SOT17 @ NAOJ

quantitative evaluation of dgs
Quantitative evaluation of DGs
  • The data used here were obtained by FPP in April 19-20, 2005 at Palo Alto.
  • 2x2 summing mode, 1Kx1K partial images
  • Magnification is different from the actual telescope, and the solar diameter is around 600 pixels (1/3 of full FOV).
  • The Doppler velocity is evaluated along the latitudinal lines at 0, 30, and 60.

Raw data of FG Dopplergram

Velocity index (R)

SOT17 @ NAOJ

slide8
The velocity profiles exhibit linear dependence on positions along the longitudinal lines as expected.
  • The velocities of the solar rotation obtained by FPP are roughly consistent with the expected one. Systematic difference is 200m/s
  • But there is time variation in the obtained velocity, and the deviation from the theoretical prediction is about 400m/s in the worst case.

SOT17 @ NAOJ

intensity ripple through wavelength scan
Intensity ripple through wavelength scan

Solar spectrum

Lamp source

SOT17 @ NAOJ

effect of the intensity ripple on dgs

Ideal

difference

with ripple

Ideal

difference

with ripple

Effect of the intensity ripple on DGs
  • The intensity ripple can be reproduced by including errors in the wide field elements of the calcite blocks in TF.
  • The relation between the velocity indexes and the Doppler velocities is reexamined using the TF profiles including the ripple. The deviation from the ideal case is 1 km/s in the worst case.

SOT17 @ NAOJ

errors caused by i ripple and satellite revolution
Errors caused by I-ripple and satellite revolution
  • Fine tuning of the wavelength against solar originated absorption lines is important for deriving physical parameters from the obtained data by NFI. Adjustment of TF wavelength is performed in FPP by using Doppler velocities value calculated in MDP.
  • The largest velocity is caused by the revolution of the satellite around the earth. The maximum velocity is 3.9 km/s in a period of about 95mins.
  • In the worst case, about 1 km/s velocity offset is produced by the intensity ripple.

Simulated error of the Doppler velocities caused by the intensity ripple and the Doppler motion of the satellite.

SOT17 @ NAOJ

fov non uniformity
FOV non-uniformity
  • Full-FOV DG with 2x2 summing
  • The solar diameter is 1.5 times larger than FOV
  • Velocity profiles along the latitudinal lines show relatively large FOV non-uniformity than expected.

SOT17 @ NAOJ

calibration of the intensity ripple
Calibration of the intensity ripple
  • When the intensity ripple is caused by the halfwave plates in the calcite blocks, the intensity modulation can be represented as a function of the motor positions (provided by encoders) of the tuning elements.

: Motor positions corresponding to ith calcite block

: Intensity amplitude for ith calcite block

(Position dependent)

: Phase of the motor position for ith calcite block

(Position dependent)

ai (x,y) and bi(x,y) will be stored in the data base.

SOT17 @ NAOJ

5576a amplitude and phase map
5576A: Amplitude and phase map

Phase

Amplitude

Calcite-2

Phase

Amplitude

Calcite-3

Phase

Amplitude

Calcite-6

SOT17 @ NAOJ

spectra after calibration of i ripple 5576a
Spectra after calibration of I-ripple: 5576A

Fe I 5576A

Black: Measured

Red: Atlas +TF ideal profiles

Black: After corrected

Red: Atlas +TF ideal profiles

SOT17 @ NAOJ

position dependent lut
Position-dependent LUT
  • Dopplergram FITS data will have the motor positions of the tuning elements for the 4 exposures.
  • From the motor positions in a FITS data and the stored I-ripple function (amplitude and phase), generate a position-dependent look-up-table.
  • Doppler velocity: V(R, X, Y)

Y

Velocity

V index

X

R: Velocity index

(X, Y): Position in FOV

SOT17 @ NAOJ

dg after i ripple calibration
DG after I-ripple calibration
  • Velocity offsets and linearity areimproved.
  • More improvement might be possible.

Before calibration

After calibration

SOT17 @ NAOJ

current status
Current status
  • The data sets necessary to build the calibration function were obtained in the ground-based test.
  • The preliminary calibration data base and the S/W to generate the position-dependent LUT have been produced, but are still necessary to be tested.

SOT17 @ NAOJ