XRT-MDP Functions- AEC·ARS·FLD -

Masumi ShimojoNobeyama Solar Radio Observatory

4th Solar-B Science Meeting 2003/02/04@ISAS

XRT-MDP FunctionsMDP (onboard Mission Data Processor) analyzes

images that are observed with XRT and carries out the following XRT functions.

AEC: Automatic Exposure Control Achieve the proper exposure level.

ARS: Automatic Region Selection Select regions suitable for observations.

FLD: FLare Detection Detect flare occurrences and radiation belt

Automatic Exposure Control (AEC) AEC is the function to archive the proper

exposure level and the proper X-ray analysis filter by onboard image analysis.

AEC controls the following parameter. Exposure time Default filter or Thick filter

AEC function is applicable for images smaller than 256 k pixels (=512x512)

How to Judgment of Under/Over/Proper Exposure

MDP counts the number of pixels whose brightness is larger than Upper Level Threshold (ULT) and Lower Level Threshold (LLT).

Profile of Brightness

ULT

I(DN)

# of P

ixel

Profile of Brightness

I(DN)# o

f Pix

el

LLT

4095U = F(I)

I=ULT

4095L = F(I)

I=LLT

A) U > UFR : OverB) L < LFR : UnderC) A and B : OverD) Otherwise : Proper

UFR : Upper level Flux RatioLFR : Lower level Flux Ratio

Adjustments of Exposure level and Filter Level :1

MDP have the Exposure Index that correspond to the exposure time.

MDP adjust exposure time through increasing and decreasing of Exposure Index.

The increase/decrease step of Exposure index is variable.

DefaultFilter

ThickFilter

LongestExposure

ShortestExposure

ExchangePoint 2

ExchangePoint 1

01212019181716151413121110 9 8 7 6 5 4 3 2272625242322ExposureIndex

Adjustments of Exposure level and Filter Level :2

Observers define the Default and Thick filters using observing tables. Ex. Default: Thin Al filter / Thick: Thick Al filter

If exposure level exceeds the Exchange Point, AEC change the filter (Def. -> Thick / Thick-> Def.)

DefaultFilter

ThickFilter

LongestExposure

ShortestExposure

ExchangePoint 2

ExchangePoint 1

01212019181716151413121110 9 8 7 6 5 4 3 2272625242322ExposureIndex

Performance Test of AEC in the PM2 combination test :1

2002/10 PM2 combination test We test AEC function using proto-type models of MDP,

XRT electronics and CCD camera.

MDP

XRT-E

XRT-D

CCD

LED An image is taken using XRT-MDP PM2 system

LED

Performance Test of AEC in the PM2 combination test :2

Result of PM2 combination test

XRT LogicSXT Logic

LED OFF LED ON

Automatic Region Selection (ARS) ARS is the function to select region suitable

for observation by onboard image analysis. Global search

• Select the brightest region in the whole sun. Local Search

• Track the specific region. (3 regions) ARS function uses ARS patrol images.

Time resolution: One image per one orbit. Spatial resolution: 2”

(2x2 binning on CCD = 1024x1024)

Algorithm of ARS :1 (Global Search) Step1. Perform software 64 x 64 software binning to create 16 x 16 macro pixel image

Step2. Pickup four brightest macro pixels

Pick up four brightest macro pixels.

Search Region

End Address（SEV , SE H）

Start Address（SSV , SSH）

（H1 , V 1）

（H2 , V 2）

（H3 , V 3）

（H4 , V 4）

H

V

００

15

15

1024

1024

16

160,00,0

Algorithm of ARS :2 (Global Search) Step3. Determination of fine positions of the candidates

Step4. Select the fine position of the brightest region as result

16

16

V

００

255

255（h'1 , v’ 1）

（h'2 , v’ 2）

（h'3 , v’ 3）

（h'4 , v’ 4）

Total of brightness

上記マクロピクセルを中心とする32x32ピクセルの領域32

（ h'1 , v’ 1）

（ h'2 , v’ 2）

（ h'3 , v’ 3）

（ h'4 , v’ 4）

Center of brightness

32

（ H1 , V 1）

（ H2 , V 2）

（ H3 , V 3）

（ H4 , V 4）

V

００

255

255

Algorithm of ARS :3 (Local Search)

Step 1. Calculate center of brightness of the region around the position to update the position. Search size can be specified in the ARS control table.

（ v , h ）

Search Region

V

００

255

255

Center of brightness

Search Size (H)

Search Size (V)

Performance Test of ARS in the PM2 test

We simulated ARS patrol images from SXT images.

MDP analyzed these simulated images and we checked the results of the ARS function.

An Example of the results Global Search Local Search

FLare Detection (FLD) FLD is the function to detect flare

occurrence and radiation belts(SAA, HLZ). Detection of Flare occurrence Detection of Radiation Belts

FLD function uses FLD patrol image Time resolution : 10sec – 640 sec Spatial Resolution : 8”

(8x8 binning on CCD = 256x256)

Algorithm of Flare Detection:1 Step1.

Perform software 16 x 16 software binning to create 16 x 16 macro pixel image (F). Subtract weighted running image (Iav) from the patrol macro pixel image to create map of ‘q’.

ｑ ＝ (Iav－F) 1/２÷ (Iav +g)

g : Offset for avoiding to divide by 0

256

256

16

160,00,0

16

160,0

q-map

Algorithm of Flare Detection:2 Step2.

If some macro pixel have q larger than “Start threshold” for flare start, MDP set the flare flag to 1.

If all macro pixel have q smaller than “End Threshold” for flare end, MDP set flare flag to 0.

• Start Threshold > End Threshold Step3. Calculate flare position from 32 x 32 pixel centered

on the macro pixel with largest q. Subtract ‘pre flare image’ from patrol image and calculate

center its center of brightness. Step4. Update running average image with following

formula. 256－ｍ ｍ Iav ＝ × Iav＋ ×F 256 256 (m=0~256)

Radiation Belt Flag Images may be disturbed by charged

particles, when the spacecraft passes the polar region and SAA. In order to prevent unexpected behavior in automated functions, MDP have capability to set the radiation flag. When the flag is set - ARS postpones patrol exposures. AEC and FLD can change some thresholds

used in the calculation.

Algorithm of Radiation Belts Two methods to set the radiation belt(RB) flag

a) The radiation belt detection by the image analysis to FLD patrol images.

b) Command setting and based on track prediction.

H

V

００

15

15

Start Threshold

End Threshold

INOUT OUT

Performance Test of FLDin the PM2 test

We simulated FLD patrol images from SXT images. Time resolution : 30sec FLD patrol images are taken by XRT using Thick Be filter.

MDP analyzed these simulated images and we checked the results of the FLD.

An Example of the results of FLD test

The performance of FLD From PM2 performance test,

FLD function have capability of detecting > C5-7 flares, if the condition on the orbit is good.

If the time resolution of FLD patrol images is smaller than 30 second, we can detect a flare in early phase of the flare.

Note of FLD If FLD patrol images are taken every 30 sec,

the number of shutter motion is 1x106/year. If mission life is 3 years, the number corresponds to 10% of the life of shutter mechanism.