A wide field of view Gas Filter Correlation Radiometer (GFCR) has been developed to make solar occultation measurements of the vertical methane distribution in the stratosphere from a sounding rocket platform. The GFCR has demonstrated a 50° solar acceptance angle that allows for a GFCR measurement during every rotation of the payload without active orientation control. The flat surface of a plano-convex ZnSe lens was etched to diffuse the projected image of the sun. By diffusing the incident solar radiation through a wide angle, sufficient radiation could be directed to the collimating GFCR optics even when the optical axis points as far as ± 25° away from the Sun. The system can be configured to measure other gaseous species with spectral bands in the 2 - 6 μm region by simply changing the bandpass filter and the correlation gas. In a laboratory calibration, the optical density of methane in a test cell was varied from 10^-4 to 10<sup>-2</sup> atm·m as the GFCR correlation cell optical density was held at 2.5×10<sup>-3</sup> atm-m. The process showed that measurements with a signal to noise ratio > 30:1 can be expected when the system operates in altitudes from 25 to 40 km. The GFCR performed with a correlation of 99.7% to the prediction of a theoretical model created with the HITRAN database. Sensitivity to gas distributions at other altitudes can be optimized by changing the gas pressure in the correlation cell. The payload featuring the GFCR is scheduled to be launched on an Enhanced Orion sub-orbital sounding rocket from NASA Wallops Flight Facility in April 2003. Future applications include validation and truthing for space-born remote sensing systems.
An Orion sounding rocket will be launched from Wallops Flight Facility and will carry a University of Virginia payload to an altitude of 65.7 km to measure the distribution of methane in the Earth’s upper atmosphere and record images and quantitative measurements of the distribution of chlorophyll in the Metompkin Inlet, Virginia. This new payload launch will be UVa’s second launch as a result of a five-year undergraduate design project by a multi-disciplinary student group. As part of a new multi-year design course, undergraduate students designed, built, tested, and will participate in the launch of a suborbital platform from which atmospheric remote sensors and other scientific experiments can operate. The first launch included a simplified atmospheric measurement system intended to demonstrate full system operation and remote sensing capabilities during suborbital flight. The second and upcoming launch includes a methane GFCR system intended for upper atmospheric measurements, a photodiode/camera system intended for the remote sensing of chlorophyll distribution and concentration in the Metompkin Inlet due to confined animal runoff pollution. Two thermoelectrically cooled HgCdTe infrared detectors, with peak sensitivity at 3 mm, were designed to measure the methane distribution in the upper atmosphere, by having infrared radiation filtered through a methane cell and a nitrogen reference cell. A small camera with a green band-pass filter will be aligned with five photodiodes, each covered by a narrow bandpass filter that matches the filters in the SeaWiFS system, to provide cross-referencing for the remote sensing of the chlorophyll in the Metompkin Inlet and to enhance the chlorophyll distribution. This payload will serve as a platform for future atmospheric sensing experiments. Currently, the GFCR has been tested and calibrated, the chlorophyll measurement system is being calibrated, and the components and mounts are being gathered, calibrated, tested and fabricated. In the next few months, the payload will be integrated and the data reduction models will be constructed.
An Orion sounding rocket launched from Wallops Flight Facility carried a University of Virginia payload to an altitude of 47 km and returned infrared measurements of the Earth's upper atmosphere and video images of the ocean. The payload launch was the result of a three-year undergraduate design project by a multi-disciplinary student group from the University of Virginia and James Madison University. As part of a new multi-year design course, undergraduate students designed, built, tested, and participated in the launch of a suborbital platform from which atmospheric remote sensors and other scientific experiments could operate. The first launch included a simplified atmospheric measurement system intended to demonstrate full system operation and remote sensing capabilities during suborbital flight. A thermoelectrically cooled HgCdTe infrared detector, with peak sensitivity at 10 micrometers , measured upwelling radiation and a small camera and VCR system, aligned with the infrared sensor, provided a ground reference. Additionally, a simple orientation sensor, consisting of three photodiodes, equipped with red, green, and blue light with dichroic filters, was tested. Temperature measurements of the upper atmosphere were successfully obtained during the flight. Video images were successfully recorded on-board the payload and proved a valuable tool in the data analysis process. The photodiode system, intended as a replacement for the camera and VCR system, functioned well, despite low signal amplification. This fully integrated and flight tested payload will serve as a platform for future atmospheric sensing experiments. It is currently being modified for a second suborbital flight that will incorporate a gas filter correlation radiometry (GFCR) instrument to measure the distribution of stratospheric methane and imaging capabilities to record the chlorophyll distribution in the Metompkin Bay as an indicator of pollution runoff.