{"id":15076,"date":"2025-07-01T10:00:00","date_gmt":"2025-07-01T10:00:00","guid":{"rendered":"https:\/\/modernsciences.org\/staging\/4414\/?p=15076"},"modified":"2025-06-24T05:05:58","modified_gmt":"2025-06-24T05:05:58","slug":"astronomical-image-simulation-photon-modeling-algorithm-training-rubin-observatory-big-data-july-2025","status":"publish","type":"post","link":"https:\/\/modernsciences.org\/staging\/4414\/astronomical-image-simulation-photon-modeling-algorithm-training-rubin-observatory-big-data-july-2025\/","title":{"rendered":"Astronomy has a major data problem \u2013 simulating realistic images of the sky can help train\u00a0algorithms"},"content":{"rendered":"\n\n\n
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\n A simulation of a set of synthetic galaxies. Photons are sampled from these galaxies and have been simulated through the Earth\u2019s atmosphere, a telescope and a sensor using a code called PhoSim.\n John Peterson\/Purdue<\/span><\/span>\n <\/figcaption>\n <\/figure>\n\n John Peterson<\/a>, Purdue University<\/a><\/em><\/span>\n\n

Professional astronomers don\u2019t make discoveries by looking through an eyepiece like you might with a backyard telescope. Instead, they collect digital images in massive cameras attached to large telescopes<\/a>. <\/p>\n\n

Just as you might have an endless library of digital photos stored in your cellphone, many astronomers collect more photos than they would ever have the time to look at. Instead, astronomers like me<\/a> look at some of the images, then build algorithms and later use computers to combine and analyze the rest.<\/p>\n\n

But how can we know that the algorithms we write will work, when we don\u2019t even have time to look at all the images? We can practice on some of the images, but one new way to build the best algorithms is to simulate some fake images as accurately as possible.<\/p>\n\n

With fake images, we can customize the exact properties of the objects in the image. That way, we can see if the algorithms we\u2019re training can uncover those properties correctly. <\/p>\n\n

My research group and collaborators have found that the best way to create fake but realistic astronomical images is to painstakingly simulate light and its interaction with everything it encounters. Light is composed of particles called photons<\/a>, and we can simulate each photon. We wrote a publicly available code to do this called the photon simulator, or PhoSim<\/a>.<\/p>\n\n

The goal of the PhoSim project is to create realistic fake images that help us understand where distortions in images from real telescopes come from. The fake images help us train programs that sort through images from real telescopes. And the results from studies using PhoSim can also help astronomers correct distortions and defects in their real telescope images.<\/p>\n\n

The data deluge<\/h2>\n\n

But first, why is there so much astronomy data in the first place? This is primarily due to the rise of dedicated survey telescopes. A survey telescope maps out a region on the sky rather than just pointing at specific objects.<\/p>\n\n

These observatories all have a large collecting area, a large field of view and a dedicated survey mode to collect as much light over a period of time as possible. Major surveys from the past two decades include the SDSS<\/a>, Kepler<\/a>, Blanco-DECam<\/a>, Subaru HSC<\/a>, TESS<\/a>, ZTF<\/a> and Euclid<\/a>.<\/p>\n\n

The Vera Rubin Observatory<\/a> in Chile has recently finished construction and will soon join those. Its survey begins soon after its official \u201cfirst look\u201d event on June 23, 2025<\/a>. It will have a particularly strong set of survey capabilities. <\/p>\n\n

The Rubin observatory can look at a region of the sky all at once that is several times larger than the full Moon, and it can survey the entire southern celestial hemisphere every few nights. <\/p>\n\n

\n \"An<\/a>\n
\n The Vera Rubin Observatory will take in lots of light to construct maps of the sky.<\/span>\n Rubin Observatory\/NSF\/AURA\/B. Quint<\/a>, CC BY-SA<\/a><\/span>\n <\/figcaption>\n <\/figure>\n\n

A survey can shed light on practically every topic in astronomy. <\/p>\n\n

Some of the ambitious research questions include: making measurements about dark matter<\/a> and dark energy<\/a>, mapping the Milky Way\u2019s distribution of stars, finding asteroids<\/a> in the solar system, building a three-dimensional map of galaxies in the universe, finding new planets outside the solar system<\/a> and tracking millions of objects that change over time, including supernovas<\/a>.<\/p>\n\n

All of these surveys create a massive data deluge. They generate tens of terabytes every night \u2013 that\u2019s millions to billions of pixels collected in seconds. In the extreme case of the Rubin observatory<\/a>, if you spent all day long looking at images equivalent to the size of a 4K television screen for about one second each, you\u2019d be looking at them 25 times too slow and you\u2019d never keep up. <\/p>\n\n

At this rate, no individual human could ever look at all the images. But automated programs can process the data. <\/p>\n\n

Astronomers don\u2019t just survey an astronomical object like a planet, galaxy or supernova once, either. Often we measure<\/a> the same object\u2019s size, shape, brightness and position in many different ways under many different conditions.<\/p>\n\n

But more measurements do come with more complications. For example, measurements taken under certain weather conditions or on one part of the camera may disagree with others at different locations or under different conditions. Astronomers can correct these errors \u2013 called systematics \u2013 with careful calibration or algorithms, but only if we understand the reason for the inconsistency between different measurements. That\u2019s where PhoSim comes in. Once corrected, we can use all the images and make more detailed measurements.<\/p>\n\n

Simulations: One photon at a time<\/h2>\n\n

To understand the origin of these systematics, we built PhoSim<\/a>, which can simulate the propagation of light particles \u2013 photons \u2013 through the Earth\u2019s atmosphere and then into the telescope and camera.<\/p>\n\n

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