Guidance for Using NEOWISE Data for NEA Observations
Originally Posted: October 14, 2024
In October 2024 I presented a poster at the annual meeting of the Division for Planetary Sciences. This poster was an offshoot of my larger work and was designed to provide some easy to follow guidance for others in the small bodies community. The work may or may not end up published on its own, so I wanted to share it here.
Plain Language Summary
As part of my research, I work a lot with data from the NEOWISE spacecraft. This spacecraft observed a lot of asteroids, and many people in our field use its data. However, processing the data - going from the raw pictures the telescope took to data we can actually work with - is not a straightforward process. All of the required steps are laid out in special documents provided by the people who made the mission, but those documents are very long and the information can be hard to find. After years of working with NEOWISE data, we learned (often the hard way) everything that is needed to properly work with this data. Looking at what other people have published about this data, we can tell that not everyone knows everything they need to do to process the data correctly. This poster summarizes all of that information in one easy to find place.
Science Abstract
The WISE and NEOWISE missions are a key source of thermal data of near-Earth asteroids (NEAs). This spacecraft is a space-based platform that produces thermal images that originally observed in four bands, W1-W4 with effective wavelengths of 3.4, 4.6, 12, and 22 microns respectively (Wright et. al. 2010). However, since the depletion of cryogenic coolant in October 2010, the spacecraft can only observe in bands W1 and W2. These bands are now operating at higher temperatures and are affected by decreased sensitivities. Both bands, and W1 especially, are also difficult to interpret because at these wavelengths light contains thermal and reflected components and NEAs are intrinsically dimmer. Thus, careful data analysis methods are crucial when working with these data.
Detailed information on how to best work with NEOWISE data can be hard to find for users unfamiliar with the mission. Most of the required information is well documented in the mission Explanatory Supplements (Cutri et. al. 2015), however locating that information can be difficult. Furthermore, some details, such as specifics about color corrections, are not fully explained. This is evidenced by the fact that many papers that use NEOWISE observations offer little or no explanation of methods for data retrieval, processing, and analysis, all of which can drastically affect the final results. Therefore, our goal is to share some of our "lessons learned" from working with NEOWISE data and provide an easily accessible roadmap for others unfamiliar with NEOWISE data.
We first give a basic outline of how we retrieve and process NEOWISE data. We discuss the retrieval process for moving objects that ensures one is getting real detections of the object in question. This involves finding tracklets verified by the Minor Planet Center and using only those frames. We also discuss additional checks, such as manual image inspection, that we found necessary to ensure data quality, beyond consideration of the data quality flags. We then discuss the process of applying color corrections to the data. Methods for dealing with color corrections vary in the literature, and they are a potentially significant source of uncertainty. We find that incorporating additional uncertainty into the final error budget based on the color correction temperature is required. Finally, we discuss some other sources of uncertainty and, if possible, how they can be treated. We hope that this accounting will help users new to the NEOWISE data better understand and avoid potential pitfalls of working with this data set, and thus continue to leverage this rich data set for as much information as possible.