Principal Investigator: Jeng-Hwa Yee, Johns Hopkins University Applied Physics Laboratory

Proposal Title: Development of a Self-Calibrating Instrument for Monitoring Ozone and Water Vapor

SCH₂OO₃NERS (Self-Calibrating H₂O and O₃ Nighttime Environmental Remote Sensor) is a compact, integrated UV-IR spectrograph and imager to measure the varying absorption of starlight as the star sets through the nighttime Earth’s atmosphere to determine vertical profiles of atmospheric constituents. SCH₂OO₃NERS can provide up to 300 vertical profiles each day of ozone, water vapor and nitrogen dioxide as well as the state variables density, pressure and temperature as a function of altitude, yielding daily global 3-D maps of these observables.

This stellar occultation technique has recently been demonstrated to be viable using data from the Ultraviolet Imagers and Spectrographic Imagers (UVISI) on the Midcourse Space Experiment (MSX) satellite. SCH₂OO₃NERS is an optimized instrument specifically designed to implement this technique. It is self-calibrating and suitable for long-term monitoring of ozone and other constituents in the lower stratosphere and upper troposphere. It provides its own high- precision pointing control and knowledge, required for accurate retrieval in the lower atmosphere. SCH₂OO₃NERS employs a state-of-the-art image tracking and motion compensation mechanism to correct for spacecraft pointing uncertainty. This, coupled with its small size and required spacecraft resources, makes it suitable for deployment on existing and future commercial spacecraft platforms as an instrument-of-opportunity after the year 2002.

We propose to demonstrate the capabilities of SCH₂OO₃NERS and reduce future development risk by:

1. continuing the preliminary design of the flight version of SCH₂OO₃NERS;
2. defining the spacecraft interface and resource requirements;
3. constructing a limited engineering model of SCH₂OO₃NERS for the purpose of testing and evaluating key subsystems.

We propose a six-phase, 29-month program in which we will perform risk reduction on the least developed components of SCH₂OO₃NERS, primarily the star tracking system and associated software. We will integrate these into a complete optical system and demonstrate that it meets the tracking, pointing, and imaging requirements.