Sentry

The Keo Sentry is the classic workhorse of all-sky auroral and airglow imaging. These imagers have been produced and deployed worldwide since the early 1990s. This highly sensitive instrument is field-proven and robust, ideal for autonomous operation and deployment at remote locations.

There are two main classes of the Keo Sentry. The Sentry3 leverages 3-inch diameter optics/filters and the Keo Sentry4 uses 4-inch diameter optics/filters. Sensitivity scales with the diameter of the optics and the size of the imaging sensor. In general, Sentry3 is preferred for auroral studies, while the Sentry4 is uniquely suited for sub-visual airglow studies.

Through careful optical design, all-sky imaging at speeds as fast as f/0.95 is achieved through narrow-band interference filters. The instrument can be fitted with a variety of deep-cooled scientific-grade imaging sensors.

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Ultra-Fast All-Sky Imaging

Up to f/0.95 effective all-sky imaging through narrow-band interference filters.

Flexible Filter Configurations

Available with a 6- or 8-position filterwheel, or with a single-filter drawer.

Reliable and Safe Operation

A high-reliability capping shutter acts as a bright-light protection mechanism to protect filters from solar exposure during daytime.

Powered by Synopticx Software

The included GUI-based Synopticx automatic ephemerides-driven instrument control & data acquisition Windows software ensures a truly ‘turn-key’ solution. Linux instrument control software (command-line based imaging daemon) available upon request.

Field of View: In addition to the standard fisheye field-of-view (180°), a wide range of field-replaceable field-of-view modules are available, ranging from 8° to 90°. These can be useful for high spatio-temporal resolution studies and cross-scale investigations. Custom field-of-view modules can be provided, upon request.

Number of Filters: Keo Sentry scientific imagers can be configured with a single-filter drawer or a filter wheel with 6 or 8 filter positions. Keo Scientific’s filter wheels are robust and designed to operate reliably for 10+ years in the field. Interference filters are essentially etalons and thus performance is affected by ambient temperature. All Keo filter wheels are carefully temperature-stabilized to within ±0.1°C with internal trim heating (and optional cooler) for optimum filter performance.

Imaging Sensor: Sensor-head options include a range of “Scientific Grade” back-thinned EMCCDs and CCDs with quantum efficiencies better than 95% and maintenance-free thermoelectric cooling to -70°C or better. Sensors with deep-depletion or anti-fringing technologies eliminate or suppress “etaloning” effects in the NIR. CCDs are generally preferred for long-exposure airglow measurements, while EMCCDs are ideal for high temporal resolution auroral studies.

Specifications are highly configuration dependent, some pertinent technical specifications for typical configurations are below. Please contact Keo Scientific for specifications for configurations not listed here.

	Sentry3 w/ 1024 (13.3mm) Sensor			Sentry4 w/ 2048 (26.6mm) Sensor
Field of View	8°	30°	180°	15°	30°	180°
Angular Resolution (center of field)	<0.01°	<0.03°	<0.2°	<0.01°	<0.02°	<0.09°
Spatial Resolution (100km altitude @ zenith)	<20 m	<60 m	~300 m	<15 m	<25 m	~150 m
Effective f-number	f/0.95			f/1.2
Filter Diameter	3 inches			4 inches
Filter Positions	1, 6, or 8
Filter Switching Speed	<1 sec between adjacent positions
Filter Thermal Stability1	±0.1°C
Minimum filter bandwidth (FWHM)	2.0 nm			1.8 nm
Capping Shutter Reliability	>1,000,000 open/close cycles
Software	Synopticx Data Acquisition and Control Software
Operating Environment	0 C to +30 C, non-condensing
Dimensions (typical, L x W x H)	Single Filter: 75 x 15 x 18 cm Multi-Filter: 75 x 30 x 35 cm			Single Filter: 85 x 18 x 21 cm Multi-Filter: 85 x 40 x 42 cm
Weight	Single Filter: 10 kg Multi-Filter: 15 kg			Single Filter: 14 kg Multi-Filter: 20 kg