Radiation Budget Instrument (RBI) is a scanning radiometer that measures earth reflected solar radiance and thermal emission at the top-of-atmosphere. RBI has three radiance channels that cover 0.25-5μm, 5-100μm and 0.25-100μm spectral bands respectively. To ensure highly accurate measurement throughout mission life, RBI is equipped with two internal calibration targets to routinely calibrate the radiance channels on orbit. A highly stable Electrical Substitution Radiometer (ESR) based Visible Calibration Target (VCT) is used to calibrate RBI short wave and total channel; A 3- bounce specular trap blackbody Infrared Calibration Target (ICT) with high emissivity, High accuracy temperature measurement is used to calibrate the RBI long wave channel. Prior to launch, RBI will undergo a comprehensive ground calibration campaign in a thermal vacuum chamber developed for RBI at the Space Dynamics Laboratory (SDL). A set of calibration targets developed by SDL, including short wave radiance source (SWRS), long wave infrared calibration source (LWIRCS), and a space view simulator (SVS) were used for RBI ground calibration. The plan is to characterize RBI absolute radiance measurement accuracy and repeatability, tie internal calibration targets to ground calibration, to carry the ground calibration to orbit. In fall 2017, the RBI Engineering Development Unit (EDU) went through the ground calibration campaign, as the pathfinder for flight unit. A large discrepancy was observed between the SDL target based calibration and RBI internal target based calibration. In this paper, we describe the discrepancy observed, the root cause analysis, and some lessons learned.
Remote sensing using mid-infrared wavelength has many applications in pollution surveillance and atmosphere studies. However, high gain, low noise detectors or single photon counters are not available in the mid-infrared wavelength range. One approach to obtain single-photon detection in mid-infrared wavelength is to convert the mid-infrared radiations into visible/near-infrared wavelengths where high efficiency and low dark current detectors are easily available. In this paper, the up-conversion of mid-infrared radiations based on the quasi-phase matching condition of periodically poled lithium niobate (PPLN) is investigated. The bandwidth and efficiency are the two essential parameters for the up-conversion process. The optimal pump wavelength λlasero and PPLN period Λ can be determined from conservations of energy and momentum. Once the λlasero and Λ are defined, the spectral bandwidth corresponding to the full width at half maximum of frequency up-conversion can be calculated. The spectral bandwidth of mid-infrared radiations can exceed 130 nm for a 25 mm PPLN crystal when the pump laser operates in the optimum wavelength. It is wide enough to cover both the on and off wavelengths of the species of interest in a Differential Absorption Lidar. The maximum up-conversion bandwidth usually corresponds to the longest PPLN period allowed by the quasi-phase matching condition. The conversion efficiency increases with the pump laser intensity. Both the external cavity pumping approach with cavity locking technique and the intra-cavity pumping approach can greatly increase the up-conversion efficiency.
A tunable continuous-wave (CW) intracavity pumped periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) has been developed where a diode-pumped ring-cavity Nd:YAG laser is used as the pumping source. The idler tunable range from 2.3 μm to 3.9 μm with linewidth less than 15 MHz has been demonstrated. The slop efficiency of the idler output versus the diode pump power is ~ 5.6%. The idler output power at 3.4 μm reaches 370 mW when the diode output power is 21.5 W. The PPLN OPO will be applied to seed ZnGeP2 OPO pumped by a Tm:Ho:YLF laser (λ=2.05 μm). The ZnGeP2 OPO can be tuned between 3-10.5 μm. Combined PPLN OPO and ZnGeP2 OPO, the tunable range covers the strong absorption lines of most atmospheric pollutants, and overlaps the mid-infrared atmospheric windows of 3.4-5 μm and 8-13 μm. The mid-infrared emission source is a potential lidar transmitter for remote sensing applications.
We are developing a high energy, narrow linewidth, and tunable mid-IR laser source that can be used to measure the green house gases and toxic gases with sufficient sensitivity and accuracy. This system consists of three major components; a high energy seeded 2.05-micron pump laser, a parametric oscillator and amplifier tunable between 3 to 9 microns and a continuous wave Periodically Poled Lithium Niobate (PPLN) seed source for parametric oscillator. A high-energy 2.05-micron pump laser with 600-mJ output has been demonstrated. This laser is comprised of one oscillator and two amplifiers. It is operated in a double pulse format to increase the system efficiency. The high beam quality combined with the narrow linewidth feature makes it a superior pump source for the parametric oscillator and amplifier. A seed source for the parametric oscillator can be implemented by using a PPLN continuous wave Optical Parametric Oscillator (OPO). The efficiency of this PPLN OPO can be greatly increased because of the huge nonlinearly associated with the d33 element of the nonlinear tensor of this material and the non-critical phase matching. Recent significant material growth improvement of ZnGeP2 makes it possible to produce the crystal with sufficient low absorption at the 2.05 pump wavelength (<0.1cm-1). This crystal also has the characteristics of wide transparency range and large second-order nonlinearities. Such a crystal is one of the most promising nonlinear optical materials for efficient frequency conversion into the mid-IR spectral region. In this paper, the design and preliminary results of this laser system will be presented.
Current results from laboratory testing of an eye-safe, ground-based ozone lidar instrument specialized for ozone differential absorption lidar measurements in the troposphere are presented. This compact prototype instrument is intended to be a prototype for operation at remote field sites and to serve as the basic unit for future monitoring projects requiring multi-instrument networks. In order for the lidar to be widely deployed, it must be fairly easy to use and maintain as well as being cost-competitive with a ground station launching ozone sondes several times a week. To achieve these goals, the system incorporates (1) an all- solid state compact OPO transmitter, (2) a highly efficient, narrow bandpass grating-based receiver, (3) dual analog and photon-counting detector channels, and (4) a PC-based data acquisition system.
The development of a portable, eye-safe, ground-based ozone lidar instrument specialized for ozone differential absorption lidar (DIAL) measurements in the troposphere is presented. This compact prototype instrument is intended to operate at remote field sites and to serve as the basic unit for future monitoring projects requiring multi-instrument networks. In order for the lidar technology to be widely deployed in networks, it must be fairly easy to use and maintain as well as being cost-competitive with a ground station launching ozone sondes several times a week. The chosen laser transmitter for the system is an all-solid state tunable frequency-doubled OPO which produces 25 mJ uv pulses. Progress with alternative solid-state uv laser sources based upon an IR-pumped OPO and based upon stimulated Raman scattering in barium nitrate will be discussed. The receiver incorporates highly efficient dielectric coatings, a parabolic primary and a narrow- bandpass grating-based filter. Dual analog and photon-counting detector channels are incorporated to extend the measurement range. All data acquisition and control hardware is incorporated in an industrial PC-based system. A flexible, user-friendly graphical user interface is written in LabVIEW for data acquisition and online processing and display.
A technique is described that precisely controls the spectral resonance wavelength of Bragg grating before they are written onto an optical fiber. The Bragg reflector filters can then be produced at any desired wavelengths.