Abstract
Abstract. This paper describes the All Sky Infrared Visible Analyzer (ASIVA), a multi-purpose visible and infrared sky imaging and analysis instrument whose primary function is to provide radiometrically calibrated imagery in the mid-infrared (mid-IR) atmospheric window. This functionality enables the determination of diurnal fractional sky cover and estimates of sky/cloud temperature from which one can derive estimates of sky/cloud emissivity and cloud height. This paper describes the calibration methods and performance of the ASIVA instrument with particular emphasis on data products being developed for the meteorological community. Data presented here were collected during the Solmirus' ASIVA campaign conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Climate Research Facility from 21 May to 27 July 2009. The purpose of this campaign was to determine the efficacy of IR technology in providing reliable nighttime sky cover data. Significant progress has been made in the analysis of the campaign data over the past several years and the ASIVA has proven to be an excellent instrument for determining sky cover as well as the potential for determining sky/cloud temperature, sky/cloud emissivity, precipitable water vapor (PWV), and ultimately cloud height.
Highlights
Where IλSky = Instrumental Counts measured for the sky image, IλRef = Instrumental 5 Counts measured for the reference blackbody image, Gλ = Instrument response coefficients derived from Eq (1), and BBλ (TRef) = Integrated Blackbody Radiance derived from Eq (2) for ambient temperature TRef
As a verification of these procedures, All Sky Infrared Visible Analyzer (ASIVA) spectral radiance data were compared with the precisely calibrated data retrieved from the Atmospheric Emitted Radiance In20 terferometer (AERI) instrument available for the campaign period
Second-order analysis is implemented in the ASIVA instrument 15 but was not used in the analysis presented below as it was not used in the dataset retrieved from the Atmospheric Radiation Measurement (ARM) archive
Summary
The ASIVA instrument (shown in Fig. 2) was deployed at the ARM SGP site from 5 21 May to 27 July 2009 The IR camera provided image data at 14-bit resolution and at a 30 Hz 10 rate. Sixteen of these images were co-added to produce a single frame with an effective exposure of 0.53 s. The visible camera provided 15 image data at 10-bit resolution and exposures up to 2 min in length. The hatch was opened wherein one visible and two infrared sky images were acquired until the data acquisition sequence. The ASIVA IR image is a single frame (0.53 s exposure) image and demonstrates that the sun’s presence 10 has almost no impact on the image
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