Small-Sat Lidar Sea Surface Vector Winds and Height Measurements System
Lead PI: Ozdal Boyraz, University of California Irvine
Start Year: 2018 | Duration: 2 years
Partners: NASA , Jet Propulsion Laboratory
Series of satellite and airborne missions for long-term global observations of the land surface, biosphere, solid Earth, atmosphere, and oceans have been dispatched to improve the understanding of the Earth as an integrated system. Up to date, a wide range of airborne and satellite instruments from microwave to optical systems have been utilized to achieve this goal. However, these satellites and instruments are usually bulky and power-hungry devices. The main objective of this proposal is to develop standalone small spacecraft technology that can play a vital role in achieving small, affordable and transformative approaches to enable remote sensing systems for littoral variables such as sea surface vector winds, sea surface height etc., without sacrificing performance metrics that are achieved in conventional space and airborne technologies. The proposed design particularly targets reduced size and power consumption while achieving specified target accuracies. In particular, the proposed effort aims for a small form factor that can fit in 6U CubeSat dimensions (4x8x12 inches), it is lightweight and low power (<100W).
There are several design challenges to be addressed when reducing the size of conventional satellites into a very small form factor. The first task will address how to design a multi-aperture telescope to scan multiple directions along the satellite track. The proposed work will design develop three aperture telescope system at 1064nm for vector wind measurement. The three apertures will be able to scan up to ±4˚ independently to measure sea surface vector wind and to achieve 60km cross-track measurement. With careful design of the telescope, beam diameter (FWHM) will be kept below 30m to achieve a satisfactory resolution. The second task will focus on adding electronic beam steering by using MEMS reflectors. Currently, the PI and Co-Is at the Jet Propulsion Laboratory are developing an omnidirectional optical communicator (OOC) for CubeSats using MEMS technology. They will build on the expertise gained on the CubeSat OOC project and investigate adding liquid crystal based optical phased arrays and MEMS mirrors to achieve wider scanning angles and also to increase the number of azimuth angles at faster refresh rates. The proposed system, based on phased array beam steering system, will be able to measure horizontal and vertical wind speed up to 100m/s with 1m/s accuracy as well as horizontal and vertical wind direction in the 0-360 degree range with <5˚ accuracy. Also, the proposed work will develop an Avalanche Photo Diode (APD)-based coherent detection scheme for low noise detection. In addition to the optomechanical design that fits in small form factor, the proposed work will develop a new altimetry by using multiple tone RF modulation and spectral measurement techniques. The goal of the proposed method is to improve conventional altimetry based on time of arrival measurements.
Both UC, Irvine and JPL teams are actively collaborating on a similar Cube-Sat project for NASA. The proposed work is compatible for future upgrades, it has the potential for opening new frontiers in the Office of Naval Research’s goals in improving knowledge of the ocean. For instance, by using a compact frequency doubling and quadrupling crystals the proposed design become germane to new developments of two or three wavelength diverse lidar measurements, without sacrificing the size and geometry. Moreover, one of the challenges in satellite missions is the launching cost, which is proportional to the payload mass. The proposed design can be instrumental for future deployments that include arrays of small satellites that constantly provide a seamless surveillance of the earth’s surface and atmosphere at a cost of a single large satellite. In this proposal, we aim at a swath of 50 km from a satellite at ~400km altitude. Increasing the satellite numbers will multiply the effective swath and provide wide area scanning capabilities.
The proposed work will start in January 2018 and continue for 24 months to develop a working prototype for flight missions.