Validation of the Landsat 7 Long-term Acquisition Plan

The launch of Landsat 7 on April 15, 1999 ushered in a new era of managing global survey missions. For the first time (for Landsat or any similar mission) an automated Long-Term Acquisition Plan (LTAP) was employed to populate the US Archive at the USGS EROS Data Center. The automated LTAP system was designed to globally collect sunlit, essentially cloud-free, and seasonally refreshed Landsat acquisitions for all land areas of the Earth. The LTAP has successfully populated the archive such that most users requiring data find it already in the archive, from the right time of year, substantially cloud-free, and under the right radiometric conditions, rather than having to order new acquisitions. Requests for data acquisitions outside of the LTAP have been lower than for any other Landsat mission. After three years of operations, we have undertaken an exhaustive analysis of the performance of the LTAP in terms of seasonality, cloud contamination, gain setting strategy, and satisfaction of science community requirements. This paper addresses the evolution of the LTAP during Landsat-7 operations, the validation strategies that were designed, and the results of the validation process. In addition, lessons learned from the validation exercise and future updates to the LTAP strategy are discussed. INTRODUCTION AND BACKGROUND A new automated approach to Landsat mission operations was introduced with the deployment of Landsat 7. A long-term acquisition plan (LTAP) was developed prior to launch to systematically populate the US archive, held at the USGS EROS Data Center, with seasonally refreshed, essentially cloud-free observations of all land areas of the planet (Arvidson, et al, 2001). The LTAP system addresses terrestrial seasonality, cloud climatology versus daily NOAA-predicted cloud cover, the two possible gain states on the Enhanced Thematic Mapper plus (ETM+) sensor on Landsat 7, and various technical and/or operational constraints such as sensor duty cycle and battery reserve