Arecibo Optical Facility (AOF)

Space & Atmoshperic Sciences

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Discovery science is the future of the passive optics research facility at Arecibo Observatory (AO), just as it has been the legacy. The optical instruments at AO have been collecting high quality optical data since the 1960s.

Mission The mission of the Arecibo Optical Laboratory (AOL) and its Remote Optical Facility is to continually improve the research-to-operations (and its reciprocal) data collection and dissemination necessary to address urgent national enterprises as Space Weather forecasting and Climate Change investigations.

Current Status Neither the AOL nor the ROF have suffered damage to infrastructure or instrumentation during the Gordon Telescope calamity in December 1, 2020. Both sites have continued to acquire data during this time, through remote or staffed operation.


The Arecibo Optical Laboratory (AOL) sits in a karst saddle at the Arecibo Observatory (AO), protected from direct light pollution to the horizon. It is located below the LIDAR facility hill to the North, and beneath the RFI monitoring hilltop to the South. The receiver testing building adjacent to the LIDAR lab and above the AOL also houses passive all- sky optical imagers (ASI) with views to the horizon.


Instrumentation at the AOL is a mixture of the original, custom aeronomy instruments, and modern internet-aware instruments recently established. The original instruments are of classical, finely machined vintage. These instruments include a 1-m Ebert-Fastie spectrometer with near ultraviolet to near infrared capability and two dual channel tilting filter photometers. These instruments are owned by observatory management, and unfettered transfer has occurred with each management transition.

Instruments that have been added to the AOL since the mid-1980s have been placed through informal public-private or public-academic partnerships. These instruments have been categorized as “User Owned Public Access” (UOPA) resources. This model has successfully maintained state-of-the-art, discovery quality instruments at the federal facility as resources to the entire community. User owners of passive optical equipment include Boston University, Penn State University, The Applied Physics Laboratory (APL), and Computational Physics Inc. (CPI).

  • Dual Channel Tilting-filter Photometers

    Measure airglow intensities in the visible and near-infrared wavelengths. A combination of filters can be used to simultaneously study the intensity distribution of several different airglow emission features. Typical filter bandwidths range between 0.3 and 1.0 nm, which is considered as coarse resolution. The field-of-view of is variable between 2.5o and 5.0o by selecting suitable field stops. Observations are scheduled regularly every month during new moon periods. In general, they are set to measure emissions at the wavelengths of 557.7-nm and 630.0-nm or 656.3-nm and 844.6-nm, but measurement at other wavelengths such as that molecular Nitrogen is also possible. During the observation period, the photometer is calibrated for absolute brightness using the 14C source.

  • Ebert-Fastie Spectrometer

    The Ebert-Fastie Spectrometer: can sample airglow emissions in the ultra-violet to the near-infrared wavelengths (between ~ 300-900 nm) over a narrow or broad wavelength range and at medium to high spectral resolution. The maximum (second order) scan range is about 100 nm. Practical limits of spectral resolution range between 0.02 and 1.0 nm. Field-of-view of this instrument could be varied between 0.1o and 9.0o by changing the entrance slit size. Observations are scheduled regularly every month during new moon periods. Regular calibration with Tungsten and Hydrogen lamp sources is performed to check performance. Since the hurricane Maria in 2017, the observations with the spectrometer are not optimized due some damage. Currently, the AO team is working on the repairs and update of this valuable instrument.

  • Fabry-Perot Interferometers(FPIs)

    Four FPIs are established at the AOL. Two of then contain components that are a mixture of user-owned (CPI) and AO and two others are from CPI. The upgraded redline instrument, and new dedicated 5577Å FPI channel, a Balmer-alpha specific FPI, and an IR FPI with optics optimized to 11,000Å. Each FPI system is internet aware, and performs automated or remotely operated wavelength and response calibrations. 250-300 nights of F-region wind data are now assembled each year, with observing frequency increased 10-fold form the period prior to 2012. The 6300Å FPI achieves statistical wind errors < 1 m/s and temperature errors < 15K with less than two minutes’ integration. The sensitivity and stability of this FPI is now allowing direct measurement of vertical motions in the thermosphere.


The FPIs run in daily basis. They are highly automated and perform flat fielding and spectral calibrate themselves. The products measured by the 6300Å FPI are available daily at the webpage:

All sky airglow imager systems (ASIs): The ASIs can capture the faint airglow emissions originating in the upper atmosphere. The front-end optics of an ASIs contains a fish eye lens that enables the ASAI to have 180o sky coverage. ASIs have a temperature controlled filter housing that can host multiple narrow band pass interference filters. Several different emissions can be captured by ASIs with the help of suitable filters. The AOL has three ASIs in daily operations: the Walden Small all‐sky imager owned by AO, which is a relatively low‐cost, small all‐sky fisheye spectral imager usually observes the 6300Å and 5577Å (also has three additional filter slots); the PSU ASI that offers 6300Å, 5577Å and 7774Å filters; and the BU ASI observes the 6300Å, 5577Å. 7774Å, OH 6950Å, and a background channel at 6050 (data available daily at ).


Dr. Pedrina Terra dos Santos


phone: 787 8782612 Ext 258