The temperatures of Giordano Bruno crater observed by the Diviner Lunar Radiometer Experiment: Application of an effective field of view model for a point-based data set

doi:10.1016/j.icarus.2015.10.034

Icarus

Volume 273, 15 July 2016, Pages 205-213

https://doi.org/10.1016/j.icarus.2015.10.034 Get rights and content

Highlights

•
A novel effective field of view (EFOV) model for processing LRO Diviner data.
•
Diviner data reveals details observable in the high-resolution LROC NAC images.
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Thermophysical properties of Giordano Bruno ejecta are very heterogeneous.
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Giordano Bruno has experienced minimal disruption by micrometeoroid impacts.
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Regions of high anisothermality are characterized by blocks and lower crater densities.

Abstract

Point based planetary datasets are typically stored as discrete records that represent an infinitesimal location on the target body. Instrumental effects and spacecraft motion during integration time can cause single points to inadequately represent the total area on the target that contributes to an observation. Production of mapped data products from these data for scientific analysis proceeds by binning points onto rectangular grids. Empty bins occur where data coverage is insufficient relative to grid resolution, a common problem at high latitudes in cylindrical projections, and remedial interpolation can lead to high uncertainty areas and artifacts in maps.

To address such issues and make better use of available data, we present a method to calculate the ground-projected effective field of view (EFOV) for point-based datasets, using knowledge of instrumental characteristics and observation geometry. We apply this approach to data from the Lunar Reconnaissance Orbiter (LRO) Diviner Lunar Radiometer Experiment, a visible to far-infrared multispectral radiometer which acquires radiometric measurements of reflected visible and emitted infrared radiation of the Moon in 9 spectral channels between 0.35 and 400 µm. Analysis of gridded radiance from crater Giordano Bruno, a 22 km diameter rayed crater, is used to demonstrate our gridding procedure. Diviner data, with such processing, reveals details of the surface that are seen in the high-resolution LRO Camera NAC images. Brightness temperatures and anisothermality observed in Diviner’s IR channels show the thermophysical properties of the crater ejecta to be very heterogeneous indicative of minimal mechanical disruption by micrometeoroid impacts consistent with a very young (<10 Ma) formation age as the lunar surface becomes rapidly homogenized over time. This heterogeneity has implications for crater-count studies as regions of high anisothermality are characterized by large blocks of material and lower crater densities.

Introduction

The Diviner Lunar Radiometer Experiment (Paige et al., 2010a) is one of seven instruments aboard NASA’s Lunar Reconnaissance Orbiter (LRO) (Chin et al., 2007, Tooley et al., 2010, Vondrak et al., 2010). Diviner began operating July 5, 2009, mapping the Moon on a nearly continuous basis, acquiring calibrated radiometric measurements of reflected visible, and emitted infrared radiation of the Moon in 9 spectral channels covering a wavelength range of 0.3–400 µm. Each Diviner channel is comprised of a 21-element thermopile detector array and spectral filter. The instrument nominally points in the nadir direction operating as a multi-spectral pushbroom mapper. Observations are acquired continuously with a 0.128 s signal integration period, providing a swath width of 3.4 km and a nominal instantaneous field of view (IFOV) of 320 m in-track and 160 m cross-track for each detector at an orbital altitude of 50 km.

The Diviner Commissioning and Primary Mapping dataset, covering July 5, 2009 to September 15, 2012, have been gridded into global brightness temperature maps referred to as Diviner Global Data Records (GDR), which have been archived at the NASA Planetary Geosciences Node (LRO-L-DLRE-5-GDR-V1.0) (Paige et al., 2011). These gridded data products were derived directly from the Reduced Data Records (RDR) products: level 1 calibrated radiance observations (Sullivan et al., 2013). Diviner GDR data products are not interpolated and include data gaps in grid cells where no observations were acquired.

The data gridding approach described in this paper was developed and used for the creation of all archived Diviner GDR products (Paige et al., 2011) and is routinely employed when gridding Diviner data. We therefore use Diviner as an example to illustrate our approach, though our procedure in this paper is not necessarily Diviner specific. We then present analysis of Diviner data from two orbits tracks crossing the crater Giordano Bruno showing how the thermal response of the surface material within and around the crater to solar forcing reveals a complex, and heterogeneous mixture of thermophysical properties, consistent with a very young crater that has experienced minimal processing by micrometeoroid bombardment.

Section snippets

Calculating the effective field-of-view (EFOV)

For an instrument operating in a pushbroom configuration like Diviner, the effective FOV in the in-track direction is broadened by two effects: (i) spacecraft motion relative to the target body during the sample integration time b(t) and (ii) the exponential detector thermal response time d(t). These effects result in elongation of the FOV in the in-track direction, and along with the instrument’s instantaneous field of view (IFOV) f(t), define the total contribution to an observation. Knowing

Gridding data

In determining the effective surface footprint of the detectors, the orientation of the detectors must first be determined. Fig. 3 shows the basic viewing geometry of the array of Diviner detectors. To determine their orientation relative to north, we define a plane determined by the vector from the center of the Moon to the latitude and longitude of the point observation on the surface, s, and the vector defining the lunar spin axis in the north direction N. The orientation of the detectors is

Application: Brightness temperatures at Giordano Bruno crater

Giordano Bruno is a young Copernican-age crater with a diameter of 22 km near the eastern limb on the lunar far side (36°N, 103°E). The crater has a very fresh morphology with high rock abundance values derived from Diviner (Fig. 8) and an extensive ray system that is found to be extremely immature in spectral studies (Pieters et al., 1994, Lucey et al., 2000, Grier et al., 2001). The age of Giordano Bruno is estimated to be 1–10 Ma based on the crater size–frequency distribution of small craters

Conclusions

We present a method to improve accuracy and address issues associated with binning point-based datasets. Using knowledge of instrumental characteristics and spacecraft and observation geometry, we model the effective, ground projected field-of-view for each observation prior to binning that data. The EFOV is discretized into individual points using a Monte Carlo approach. Subsequent binning with these points then provides binned data with measured values given the correct surface area

Acknowledgments

We would like to thank Karin Bauch and an anonymous reviewer for their helpful comments and the LRO, LROC, LOLA, and Diviner operations teams for the collection of high quality datasets used in this work. Support for this work was provided by the Lunar Reconnaissance Orbiter program.

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The temperatures of Giordano Bruno crater observed by the Diviner Lunar Radiometer Experiment: Application of an effective field of view model for a point-based data set

Highlights

Abstract

Introduction

Section snippets

Calculating the effective field-of-view (EFOV)

Gridding data

Application: Brightness temperatures at Giordano Bruno crater

Conclusions

Acknowledgments

Icarus

Planet. Space Sci.

Icarus

Icarus

Icarus

Lunar surface rock abundance and regolith fines temperatures derived from LRO Diviner Radiometer data

J. Geophys. Res.

Lunar Reconnaissance Orbiter overview: The instrument suite and mission

Space Sci. Rev.

Role of material properties in the cratering record of young platy-ridged lava on Mars

Geophys. Res. Lett.

Constraints on the recent rate of lunar ejecta breakdown and implications for crater ages

Geology

Highly silicic compositions on the Moon

Science

The Mairan domes: Silicic volcanic constructs on the Moon

Geophys. Res. Lett.

Global silicate mineralogy of the Moon from the Diviner Lunar Radiometer

Science

Optical maturity of ejecta from large rayed lunar craters

J. Geophys. Res.

Imaging of lunar surface maturity

J. Geophys. Res.

Formation age of the lunar crater Giordano Bruno

Meteorit. Planet. Sci.

The Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment

Space Sci. Rev.