XRT-MDP Functions — AEC ARS FLD — Masumi Shimojo Nobeyama

XRT-MDP Functions - AEC·ARS·FLD - Masumi Shimojo Nobeyama Solar Radio Observatory 4 th Solar-B Science Meeting 2003/02/04@ISAS

XRT-MDP Functions MDP (onboard Mission Data Processor) analyzes images that are observed with XRT and carries out the following XRT functions. n AEC: Automatic Exposure Control n n ARS: Automatic Region Selection n n Achieve the proper exposure level. Select regions suitable for observations. FLD: FLare Detection n Detect flare occurrences and radiation belt

Automatic Exposure Control (AEC) n n 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. n n n Exposure time Default filter or Thick filter AEC function is applicable for images smaller than 256 k pixels (=512 x 512)

How to Judgment of Under/Over/Proper Exposure n MDP counts the number of pixels whose brightness is larger than Upper Level Threshold (ULT) and Lower Level Threshold (LLT). A) B) C) D) U > UFR L < LFR A and B Otherwise : : Over Under Over Proper UFR LFR : Upper level Flux Ratio : Lower level Flux Ratio

Adjustments of Exposure level and Filter Level : 1 n n n 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.

Adjustments of Exposure level and Filter Level : 2 n Observers define the Default and Thick filters using observing tables. Ex. Default: Thin Al filter / Thick: Thick Al filter n If exposure level exceeds the Exchange Point, AEC change the filter (Def. -> Thick / Thick-> Def. )

Performance Test of AEC in the PM 2 combination test : 1 n 2002/10 PM 2 combination test n We test AEC function using proto-type models of MDP, XRT electronics and CCD camera. MDP XRT-D XRT-E LED CCD An image is taken using XRT-MDP PM 2 system LED

Performance Test of AEC in the PM 2 combination test : 2 n Result of PM 2 combination test XRT Logic SXT Logic LED OFF LED ON

Automatic Region Selection (ARS) n ARS is the function to select region suitable for observation by onboard image analysis. n Global search • Select the brightest region in the whole sun. n Local Search • Track the specific region. (3 regions) n ARS function uses ARS patrol images. n n Time resolution: One image per one orbit. Spatial resolution: 2” (2 x 2 binning on CCD = 1024 x 1024)

Algorithm of ARS : 1 (Global Search) n Step 1. Perform software 64 x 64 software binning to create 16 x 16 macro pixel image 1024 0, 0 n 16 1024 0, 0 16 Step 2. Pickup four brightest macro pixels

Algorithm of ARS : 2 (Global Search) n Step 3. Determination of fine positions of the candidates n Step 4. Select the fine position of the brightest region as result

Algorithm of ARS : 3 (Local Search) n Step 1. Calculate center of brightness of the region around the position to update the position. n Search size can be specified in the ARS control table.

Performance Test of ARS in the PM 2 test n n We simulated ARS patrol images from SXT images. MDP analyzed these simulated images and we checked the results of the ARS function. n An Example of the results n n Global Search Local Search

FLare Detection (FLD) n FLD is the function to detect flare occurrence and radiation belts(SAA, HLZ). n n n Detection of Flare occurrence Detection of Radiation Belts FLD function uses FLD patrol image n n Time resolution : 10 sec – 640 sec Spatial Resolution : 8” (8 x 8 binning on CCD = 256 x 256)

Algorithm of Flare Detection: 1 n Step 1. 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’. 256 16 16 q-map 0, 0 256 0, 0 16 g : Offset for avoiding to divide by 0

Algorithm of Flare Detection: 2 n Step 2. n n 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 n Step 3. Calculate flare position from 32 x 32 pixel centered on the macro pixel with largest q. n n Subtract ‘pre flare image’ from patrol image and calculate center its center of brightness. Step 4. Update running average image with following formula. (m=0~256)

Radiation Belt Flag n 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 n ARS postpones patrol exposures. n AEC and FLD can change some thresholds used in the calculation.

Algorithm of Radiation Belts n Two methods to set the radiation belt(RB) flag a) b) The radiation belt detection by the image analysis to FLD patrol images. Command setting and based on track prediction.

Performance Test of FLD in the PM 2 test n We simulated FLD patrol images from SXT images. n n Time resolution : 30 sec 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 n From PM 2 performance test, n n n FLD function have capability of detecting > C 5 -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 n If FLD patrol images are taken every 30 sec, the number of shutter motion is 1 x 106/year. If mission life is 3 years, the number corresponds to 10% of the life of shutter mechanism.