There are three main current ground-based surveys which have microlensing as a significant or primary component of their science program, outlined here. The science produced by all of these surveys is too extensive and varied to reasonably report here; instead we recommend interested readers refer to the publications listed on the survey websites.
| Principle Investigator | Andrzej Udalski, University of Warsaw, Poland |
| Websites |
OGLE Website
OGLE Early Warning System OGLE Photometry Database OGLE Extinction calculator OGLE Collection of Variable Stars |
| Telescope aperture | 1.3m Warsaw Telescope |
| Site | Las Campanas Observatory, Chile |
| Field of view | 1.4 square degrees (OGLE-IV camera) |
| Pixel scale | 0.26 arcsec/pixel |
| Passbands | V, I |
OGLE is one of the most established surveys in microlensing, having been in continuous operation since 1992. During this time the total area footprint of the survey has dramatically increased thanks to upgrades to its primary imaging camera, now on its 3rd version. The OGLE survey is outstanding in particular for the quality of its photometry and for its long baseline of observations. This has enabled the group to compile deep reference images and catalogs of known variable stars which are used to exclude false-positive detections. As a result, OGLE issue a very reliable stream of public alerts of microlensing events in progress, which are available via their website or by subscribing to the OGLE mailing list.
| Principle Investigator | Takahiro Sumi, Nagoya University, Japan |
| Website |
MOA Website
MOA alerts |
| Telescope aperture | 1.8m |
| Site | Mt. John Observatory, New Zealand |
| Field of view | 2.2 square degrees (MOA-II) |
| Pixel scale | 0.58 arcsec/pixel |
| Passbands | Wide-band red, Bessell-V, -I |
The MOA project represents a long-standing multi-national collaboration between Japan, New Zealand and the USA, beginning in 1995 with the 0.6m Boller & Chivens Telescope, and progressing to the purpose-built 1.8m telescope in 2003, which greatly increased the survey footprint, photometric depth and resolution. MOA operates a particularly rapid-response public alert system for microlensing events and cataclysmic variable stars, available via their website and their mailing list. They have also pioneered the introduction of alerts sent to a cell phone app, available for the Android platform.
| Operated by | Korea Astronomy and Space Science Institute, South Korea |
| Director of microlensing program | Andy Gould, Max Planck Institute Heidelberg, Germany |
| Website | KMTNet Website |
| Telescope aperture | Three 1.6m telescopes |
| Sites | Siding Spring, Australia, Cerro Tololo Inter-American Observatory, Chile, South African Astronomical Observatory, South Africa |
| Field of view | 2 x 2 degrees |
| Pixel scale | 0.40 arcsec/pixel |
| Passbands | V, R, I |
KMTNet is the newest ground-based survey in microlensing and promises to be ground-breaking thanks to its combination of three wide-field telescopes at longitudinally-separated sites around the southern hemisphere. This means it can monitor microlensing survey fields 24/7 for a large part of the season, dramatically improving the photometric coverage of events and hence the probability of discovering planets. KMTNet began operations in 2013-2014, and does not issue alerts at the current time.
| Operated by | LSST Corporation |
| Lead of microlensing subgroup of science collaboration: | Rosanne Di Stefano (CfA Harvard) and Rachel Street (Las Cumbres Observatory) |
| Websites: | LSST Website LSST Microlensing Groups Website |
| Telescope aperture | 8.4m telescope, effective collecting area 6.67m |
| Sites | Cerro Tololo Inter-American Observatory, Chile |
| Field of view | 3.5 degrees in diameter |
| Pixel scale | 0.20 arcsec/pixel |
| Passbands | u, g, r, i, z, y |
LSST is currently under construction in Chile, and is due to begin full survey operations in 2023. It will conduct a very large, multi-filter imaging survey of all regions of the sky accessible from its site. Though the original survey design generally avoided imaging in the Galactic Plane due to concerns over the data reduction, this is in the process of review. LSST is designed to maximize time domain science by rapidly issuing alerts on all targets that change brightness or move within its field of view, at a rate expected to be of the order of tens of millions per night, at least at the start of the project.