1

Detection of Line-shaped Tracks in

Images with DADD

STScI

Peter R. McCulloughJul 21, 2011

2007, First Map of an Alien World, SST press release for Nature article of Knutson et al.

2009, Alien Maps of an Ocean-bearing World, ApJ title of Cowan et al.

2011, Observational Evidence of Sentient Life on an Earth-like Planet, TIPS alternative title of McCullough

How fast we are progressing…

2/11

2007, First Map of an Alien World, SST press release for Nature article of Knutson et al.

2009, Alien Maps of an Ocean-bearing World, ApJ title of Cowan et al.

2011, Observational Evidence of Sentient Life on an Earth-like Planet, McCullough (this work)

How fast we are progressing…

3/11

Jill Tarter, JHU seminar 2004-2005 Richard Stauduhar (1940-2010), mathematician

for the SETI Institute and U.C. Berkeley Space Sciences Lab, private communication 2005.

Cullers & Deans 1992, unpublished*, cited byBackus, P. R. 1993, The NASA SETI Microwave Observing project Targeted Search, in Third Decennial US-USSR Conference on SETI, ASP Conference Series, Vo. 47, p. 323.

SetiQuest.org, sonata-1.0.16.zip

* thanks to Jill Lagerstrom (and the authors) for obtaining a scanned copy of this unpublished report.

DADD brought to you by …DADD = Doubling Accumulation Drift Detection

4/11

Line-shaped streaks (from bright lights on Earth) appear in ~30% of HST WFC3 observations of the dark-side of Earth, (taken for flat fields, to be described in a future TIPS). DADD automates flagging of pixels within streaks.

5/11

DADD = Doubling Accumulation Drift Detection

M spectra, each with N channels

Requirement of slow drift: |slope| > 1

Mathematical operations:Brute force: ~2NM2

DADD: ~2 NM log2 M

DADD accumulates pairwise like the FFT ;DADD reuses sums of pixels common to multiple lines across the 2-D array.

To apply DADD to 2-D imagery, we analyze the image successively four times with rotations of 0º, 90º, 180º, and 270º in order to detect trails of arbitrary slope and origin.

N FrequenciesM

Tim

es

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DADD = Doubling Accumulation Drift Detection

0 0 continuous functions:0 1 all steps = 0 or 1 channel

00 00 0001 constant derivatives00 11 011101 1201 23

0000 00000000 11110011 11220011 22330112 23340112 34450123 34560123 4567

N FrequenciesM

Tim

es

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DADD is sensitive

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DADD is sensitive, quick,

Execution time per track identified

= 0.7 seconds per megapixel= 2.8 s for 2048x2048

9/11

DADD is sensitive, quick, and stands alone

Execution time per track identified

= 0.7 seconds per megapixel= 2.8 s for 2048x2048

C code operating on 16-bit FITS 2-D images, with an IDL wrapper to facilitate pre-processing and post-processing analysis.

(WFC3 ISR coming soon)

10/11

Summary: DADD can be used for detection of …

1. SETI signals, e.g. weak, drifting narrowband CW signal in time series of RF spectra

2. Streaks across dark-Earth flat-fields (as illustrated)3. Cosmic ray trails*4. Asteroid or satellite trails*5. Bleeding (overexposed PSF) trails* ^ 6. Slitless grism spectra* ^

* DADD is less sensitive to shorter line segments.^ DADD is probably overkill where orientation of trails is fixed and known a priori.

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