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Science with the Korean Solar Radio Burst Locator (KSRBL). Dale E. Gary & Gelu M. Nita Center for Solar-Terrestrial Research New Jersey Institute of Technology. Outline. Overview of KSRBL Topics for Study Radio spectrum for study of solar activity Burst location

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Science with the korean solar radio burst locator ksrbl

Science with the Korean Solar Radio Burst Locator (KSRBL)

Dale E. Gary & Gelu M. Nita

Center for Solar-Terrestrial Research

New Jersey Institute of Technology

KSRBL Science Colloquium

2009 Aug 24


Outline
Outline

  • Overview of KSRBL

  • Topics for Study

    • Radio spectrum for study of solar activity

    • Burst location

    • Radio frequency interference mitigation

    • Radio effects on navigation and communication systems

  • Conclusions

KSRBL Science Colloquium

2009 Aug 24


Ksrbl antenna

Yagi Feed (245

and 410 MHz)

Spiral Feed

(0.5-1 GHz)

KSRBL Antenna

Full Sun coverage

=> 2.1 m antenna

Gives 33 arcmin

at 18 GHz

KSRBL Science Colloquium

2009 Aug 24


Frequency coverage

17,500 frequency points at 1 MHz resolution

Frequency Coverage

  • Frequency range

    • 0.5-18 GHz continuous coverage, plus 245 and 410 MHz (yagi feed)

  • Frequency resolution

    • Best resolution 244 kHz (for RFI excision)

    • Target science resolution 1 MHz (4:1 compression)

  • Instantaneous bandwidth

    • 4 x 500 MHz = 2 GHz

KSRBL Science Colloquium

2009 Aug 24


Time resolution
Time Resolution

  • Full spectrum in 1 s

  • Time resolution for each sample is 25 ms, measured four times before tuning (100 ms for each tuning). - + + + - + + +

  • Takes 10 tunings to cover 18 GHz, hence 1 s to cover all bands.

  • Best resolution on a single band, nominally 25 ms, but can be changed (trade-off with data-rate and data volume).

KSRBL Science Colloquium

2009 Aug 24


RFI Excision

(this is a portion

of a single band

at full resolution)

KSRBL Science Colloquium

2009 Aug 24


Solar radio burst srb spectra
Solar Radio Burst (SRB) Spectra

  • The spectrum of SRBs reveals a great deal of information about plasma parameters (temperature, density, magnetic field strength, accelerated electron energy distribution). KSRBL is unique in its ability to combine high frequency resolution with broad frequency coverage.

  • At very high temporal and spectral resolution, additional features may appear, especially at decimetric (<3 GHz) frequencies.

  • Polarization is also important—KSRBL measures only RCP (required for burst location). A measurement of LCP is also needed—a second KSRBL?.

KSRBL Science Colloquium

2009 Aug 24


Example gyrosynchrotron spectrum

Pk 1: B = 240 G

Pk 2: B = 120 G

Example: Gyrosynchrotron Spectrum

Pk 1: Bt = 120 G

Pk 2: Bt = 60 G

KSRBL Science Colloquium

2009 Aug 24


Example high resolution bursts
Example: High-Resolution Bursts

  • Decimetric burst types, seen with similar frequency and time resolution as KSRBL

KSRBL Science Colloquium

2009 Aug 24


Burst location

alert!

safe?

possible

concern?

Burst Location

  • Motivation

    • Because of Parker spiral, particles from bursts east of central meridian are few and of low energy.

    • Particles from bursts on the west limb are of far more concern.

    • Knowing the location of the burst on the disk, especially for large flares, is important.

    • KSRBL can act as backup for spacecraft.

KSRBL Science Colloquium

2009 Aug 24


Burst location1
Burst Location

KSRBL Science Colloquium

2009 Aug 24


Board implementation
Board Implementation

  • CASPER iBOB-based 500 MHz Spectrometer

    • 2048 channels, 4 tap PFB (polyphase filter bank)

    • Accumulates power (S1) and power-squared (S2).

  • 1 GS/s (1 GHz clock), 500-1000 MHz IF

  • Settable dump times—use 25 ms

  • Output via fast-ethernet

  • Operate 4 boards in parallel, for 2 GHz total bandwidth

ADC

FPGA

KSRBL Science Colloquium

2009 Aug 24


Simplified block diagram

scale

coeff

bit

shift

P bit

select

4096-pt

FFT

Scale

RF In

ADC

PFB

BRAM

P

RAM

Serializer

P2

P

RAM

Parallel-

izer

P2

Bit select

P

Accumulator

P

Multiplier P2

P

Data Out

(ethernet)

Bit select

P2

1 GHz

clock

accum

length

P2 bit

select

bit

select

Simplified Block Diagram

  • Multiple levels of scaling to ensure sufficient precision of P and P2.

KSRBL Science Colloquium

2009 Aug 24


Spectral kurtosis rfi algorithm
Spectral Kurtosis RFI Algorithm

  • We have described the SK Algorithm previously (Nita et al. 2007, PASP 119, 805). The SK estimator provides a way to distinguish whether a single accumulation (time-frequency bin) is consistent with Gaussian noise.

  • Bins with certain kinds of radio frequency interference (RFI) are typically not Gaussian, hence the SK estimator can be used to identify and flag bins containing such RFI.

KSRBL Science Colloquium

2009 Aug 24


Spectral kurtosis rfi algorithm1
Spectral Kurtosis RFI Algorithm

  • The recipe for computing the SK estimator is very simple, and lends itself to real-time RFI excision using high-speed digital processing. To compute the SK estimator, one must accumulate sums of power and power-squared

  • The SK estimator for an accumulation over M samples is then

  • The variance of the SK estimator is so with a criterion of an accumulation in spectral channel k is Gaussian if it obeys the expression

KSRBL Science Colloquium

2009 Aug 24


Example a band with no rfi

One instantaneous (25 ms) spectrum with no RFI

Each spectral point is an accumulation of M = 6104 samples.

Occasionally (~0.13% of time)

exceeds 3s threshold

SK (=1±3s )

Example: A Band with No RFI

KSRBL Science Colloquium

2009 Aug 24


Sk estimator vs spectral power
SK Estimator vs. Spectral Power

Plot of SK vs spectral power (S1)

(very useful plot, as we will see)

Shows that SK estimator is independent

of power level—a key property.

Also, RFI decision is made based on statistics

of a single accumulation of a single spectral

channel. No “relative” comparisons needed.

SK estimator for 150 instantaneous spectra

KSRBL Science Colloquium

2009 Aug 24


Full resolution vs integrated spectrum

Clean spectrum after

frequency-binning to

target resolution

(512 spectral channels)

Same spectrum after

applying SK flags

(2048 spectral channels)

Full-resolution

dynamic spectrum

(2048 spectral channels)

Average spectrum

(3-3.5 GHz)

Full-Resolution vs. Integrated Spectrum

KSRBL Science Colloquium

2009 Aug 24


Sk estimator for non gaussian signals
SK Estimator for Non-Gaussian Signals

  • The SK estimator for a Gaussian signal is very close to 1, but what is the SK value for non-Gaussian signals?

  • One type of RFI we have simulated is a CW signal of constant amplitude, which can be used to simulate transient RFI by considering its presence or absence with some duty cycle, d.

  • Consider M contiguous samples out of which only R are contaminated by RFI of signal to noise ratio hk. This leads to an RFI duty cycle of d = R/M. For this case, the expected SK estimator value is

  • Note several interesting properties:

    • For d = ½, (50% duty cycle), the estimator is always 1

    • For d < ½ (highly intermittent RFI), the estimator is above 1

    • For d > ½ (more continuous RFI), the estimator is below 1

KSRBL Science Colloquium

2009 Aug 24


A key plot for understanding sk
A Key Plot for Understanding SK

Armed with these ideas, let’s look at bands with RFI

KSRBL Science Colloquium

2009 Aug 24


Example a band with a lot of rfi

Clean spectrum after

frequency-binning to

target resolution

(512 spectral channels)

Same spectrum after

applying SK flags

(2048 spectral channels)

Full-resolution

dynamic spectrum

(2048 spectral channels)

Average spectrum

(0.5-1 GHz)

Example—A Band with a Lot of RFI

Average of 150 spectra, each accumulated with

M = 6104 samples.

KSRBL Science Colloquium

2009 Aug 24


Why does this

RFI survive?

Previous plot was lower resolution than actual data.

Zoom in at full resolution

KSRBL Science Colloquium

2009 Aug 24


SK mimics

Gaussian

noise!

  • SK > 1

  • highly

    intermittent

  • SK < 1

  • more

    continuous

SK Estimator vs. Spectral Power

KSRBL Science Colloquium

2009 Aug 24


Sk vs power plot features
SK vs. Power Plot Features

  • Continuous RFI appears as discrete dots.

  • Intermittent RFI appears as “fountain” of points.

  • Curve of fountain likely reflects effective duty-cycle. “Accidental” 50% duty cycle can occur.

  • Multiscale SK moves points—can guard against 50% duty cycle problem.

  • Some RFI masquerades as Gaussian noise.

  • Let’s take a closer look to discover what characteristics the problem-RFI has.

KSRBL Science Colloquium

2009 Aug 24


This RFI is

untouched!

Incompletely

removed

Turns out this is

XM and Sirius

(digital satellite radio)

KSRBL Science Colloquium

2009 Aug 24


SK Estimator vs. Spectral Power

50% duty

cycle

Digital radio acts

like Gaussian noise

KSRBL Science Colloquium

2009 Aug 24


Southern California Edison

digital data link

KSRBL Science Colloquium

2009 Aug 24


6093 MHz center frequency

30 MHz BW, pointing

right at observatory.

SK Estimator vs. Spectral Power

Digital data links act

like Gaussian noise

KSRBL Science Colloquium

2009 Aug 24


Multiscale SK

KSRBL Science Colloquium

2009 Aug 24


Srb effects on navigation system
SRB Effects on Navigation System

Observed by OVSA and FST

at Owens Valley Solar Observatory

18

10

GHz

1

30 s near end of burst

OVSA and FST data of this record solar burst. Zooming in reveals the burst as composed of millions of millisecond spike bursts (electron-cyclotron maser emission). The FST data at right shows 20 ms time-resolution data, switching between right-circular (RCP) and left-circular polarization (LCP) every 4 s. The spikes are essentially 100% RCP.

System automatically switches between polarizations

KSRBL Science Colloquium

2009 Aug 24


Gps outage
GPS Outage

  • GPS satellites broadcast at 1247 and 1575 MHz, and the signal is right-circularly polarized (RCP).

  • The burst reached record flux levels at both of these frequencies, and was also RCP.

  • The direct interference of the solar flux caused receivers on Earth to loose lock on the satellites.

KSRBL Science Colloquium

2009 Aug 24


Conclusion
Conclusion

  • KSRBL is a unique instrument in its combination of high frequency and time resolution and broad frequency coverage.

  • It is a research instrument ideal for four types of study:

    • Solar radio bursts and solar activity

    • Burst location and space weather effects

    • Radio frequency interference mitigation

    • SRB effects on navigation and communication systems.

KSRBL Science Colloquium

2009 Aug 24


Conclusions re rfi
Conclusions Re: RFI

  • KSRBL has the first FPGA implementation of Spectral Kurtosis for real-time flagging of RFI.

  • The method supplies an automatic way to flag the worst intermittent RFI.

  • The SK estimator vs. S1 plot is useful for characterizing types of RFI:

    • SK < 1 is intermittent RFI, easy to remove. A few points may get through by chance hitting near 50% duty cycle.

    • Typical continuous RFI appears as small clusters, sometimes near or overlapping with SK = 1 window. Multiscale SK can be applied to address this.

    • Digital radio, digital data links, and likely digital TV are “awful”—they are both band-filling and they appear to the SK algorithm as indistinguishable from Gaussian noise.

  • Further study of digital RFI is needed.

KSRBL Science Colloquium

2009 Aug 24


Thank you
Thank You

KSRBL Science Colloquium

2009 Aug 24


Effect of incorrect precision
Effect of Incorrect Precision

  • When S1 (S2) precision is too low (LSB truncated), the effect is to raise (lower) the SK estimator

S1 truncated slightly (SK raised to 1.014)

Excessive clipping of

valid data

KSRBL Science Colloquium

2009 Aug 24


Results in too many flagged points
Results in too many flagged points

Mean of SK estimator in this case is 1.014 due to truncation of S1.

Thus, it is important to manage dynamic range using settable parameters.

KSRBL Science Colloquium

2009 Aug 24


Simplified block diagram1

scale

coeff

bit

shift

P bit

select

4096-pt

FFT

Scale

RF In

ADC

PFB

BRAM

P

RAM

Serializer

P2

P

RAM

Parallel-

izer

P2

Bit select

P

Accumulator

P

Multiplier P2

P

Data Out

(ethernet)

Bit select

P2

1 GHz

clock

accum

length

P2 bit

select

bit

select

Simplified Block Diagram

  • Multiple levels of scaling to ensure sufficient precision of P and P2.

KSRBL Science Colloquium

2009 Aug 24