Resolved Hapke Parameter maps

LROC Wide Angle Camera (WAC) color composite mosaic of the Moon, photometrically normalized using new Hapke parameter maps. Red: 689 nm, green: 415 nm, and blue: 321 nm band; latitude 55°S to 55°N, longitude -68.6° to 41.4°E.

Hiroyuki Sato

LROC News System

After nearly five years of LRO WAC observations, there are over 50 repeat multispectral observations for each ~480 by 480 m2 area on the Moon. The opening image is a new WAC RGB color composite mosaic using ~21 months of observations acquired during the 50 km quasi-circular orbit period. 

One of the most arduous tasks for any planetary remote sensing imaging experiment is photometric correction. What exactly is a photometric correction (or normalization)? When mosaicking together images acquired at different times, image boundaries are often quite obvious because the Sun was in a different position and the camera pointing angles may also have varied. Thus the apparent brightness of the surface can be very different where images overlap.

As the lighting and viewing angles change, the reflectance seen at the camera changes in a non-linear manner (below, left). Photometric normalization adjusts the relative brightness of each pixel in such a way that the apparent camera (emission) angle and the Sun angle are the same in every pixel (e.g. incidence angle (i) = 60°, emission angle (e) = 0°, and phase angle (g) = 60°, see angle geometries below, bottom). 

WAC 643 nm reflectance acquired for a 1° tile (centered at 0.5°N, 181.5°E) as a function of phase angle (top), and diagram of three photometric angles (i, e, and g) in the WAC geometry (bottom). 

For making seamless mosaics or comparing the reflectance at two remote locations, photometric normalization is imperative. Sounds simple, right? In theory the normalization should be simple. However the apparent brightness of the surface as the incidence angle changes is also dependent on grain size, state of maturity, and composition. Many studies have tried to replicate this non-linear reflectance variation for the nearside or for a sample area of the Moon. Typically these corrections work well for that particular area, but not for other portions of the Moon.

To make a global mosaic from the WAC data a new function was needed that accounted for all the variables mentioned above. But how can one account for changes in composition, for example mare vs. highlands? Since we have many complete image sets for the whole Moon, we could divide the Moon into 1° latitude by 1° longitude photometric tiles (64800 tiles). The wide field of view (60° in color mode) of the WAC results in more than 50% overlap with neighboring orbits, providing at least two (and often many more) different observations per 100-meter pixel for each spot on the Moon every month. Using LROC team member Bruce Hapke's photometric model [Hapke, 2012] (a widely applied theoretical model for planetary remote sensing), we parameterized the multispectral and multitemporal reflectance data from each tile (~30x30 km2 area; about 500,000 data points in average), resulting in the near-global Hapke parameter maps of the Moon (see next figure).

Spatially resolved Hapke parameter maps of the Moon for the 643 nm band (Figure 16 in Sato et al. [2014]). Color corresponds to (a) single scattering albedo: w, (b)(c) Henyey-Greenstein double-lobed phase function parameter: b and c, (d) shadow hiding opposition effect amplitude: BS0, (e) shadow hiding opposition effect angular width: hS. 

The opening WAC color mosaic was photometrically normalized using the Hapke correction and our derived parameter sets (shown in the maps above), achieving a beautiful seamless mosaic. The mosaic shows how well the correction works! Even better, the parameter maps tell us about the nature of the lunar surface. Each of the Hapke parameters has a physical meaning that relates to the material properties of the surface, for example the optical thickness and shape irregularity (b, c), grain size distribution (hS), and of course the albedo (w). This is the first ever resolved Hapke parameter map for any body in our Solar System - a major scientific accomplishment. 

A recently published paper, Sato et al. [2014] in the Journal of Geophysical Research: Planets, describes the detailed methodologies of processing this gigantic data set, estimations of accuracy, the specific Hapke model used, and new discoveries. 

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Note that small "holes" in the mosaic are due to shadows or saturation in the original observations.

Below is a posting for post-doc position at LLNL

The Chemical Sciences Division (CSD) in the Physical and Life Sciences (PLS) Directorate is seeking a planetary sciences postdoctoral researcher. This position requires US citizenship.  

The successful candidate will contribute to several research projects funded by NASA, as well to projects funded by the Department of Energy.  NASA related projects will address the origin and evolution of primordial Solar System condensates, primitive meteorites, lunar samples, and martian meteorites. 

The candidate is expected to have experience with  chemical separation by ion chromatography in a class 100 clean room environment, as with as with isotopic analyses by either multi-collector inductively coupled or thermal ionization mass spectrometry.  This individual will report to the Group Leader for Chemical and Isotopic Signatures.  

Send CV to Lars Borg (borg5@llnl.gov) or Ian Hutcheon (hutcheon1@llnl.gov).

Watching craters "as they happen"

A new crater on the Moon, "found among so many." The bright flash of formation for this approximately 34 meter diameter crater was captured simultaneously by two Earthbound telescopes in Spain on September 11, 2013. From LRO, before-image LROC NAC observation M1119014742L, orbit 17116, March 27, 2013; incidence 23.66° resolution 82 cm from 84.41 km, After-image LROC NAC M1149637354L, LRO orbit 21423, March 16, 2014; incidence 23.18° resolution 91 cm from 89.12 km  [NASA/GSFC/Arizona State University].

Mark Robinson

Principal Investigator

Lunar Reconnaissance Orbiter Camera (LROC)

Arizona State University

On 11 September 2013 the "Moon Impacts Detection and Analysis System" (MIDAS) camera captured a bright 8-second long flash on the central nearside of the Moon.

This was the brightest event captured so far by the MIDAS team, and they estimated that the crater should be between 46 and 56 meters in diameter.

The LROC team targeted the reported coordinates (17.2°S, 339.5°E) of the flash and acquired several images over a few months until the crater was found in images acquired on 16 March 2014 and 13 April 2014.

Strictly speaking, the 11 Sept. 2013 event was visible to the naked eye, though at nearly First Quarter the idealized reproduction above fails to account for the discriminating human eye. The illuminated east hemisphere would tend to have washed out Earthshine for all but those with the steadiest eyes. Fortunately, for at least ten years the unlit portion of the Nearside "visible" at night has been carefully monitored systematically, improving our understanding of hazards in the Near-Earth environment [NASA/GSFC/SVS].

Video sequence recording impact on the Moon's nearside in Mare Nubium. The magnitude of the explosion is estimated to have been roughly equal to that of Polaris, the North Star, and the recorded light curve following after lasted a remarkable eight seconds. Madiedo, et al. (2014) [IAA-CSIC/Universidad de Huelva].

Fortunately there was a NAC image of the target area acquired before the impact, so finding the new crater was relatively easy once an "after" image with comparable lighting to the "before" image was acquired.

As it turns out the new crater is ~34 meters (112 feet) in diameter and is located at 17.167°S, 339.599°E, only 2 kilometers (1.2 miles) from the original telescope-based prediction. In the before-after animation you can see ejecta effects from the crater extend out more than 500 meters in all directions!

See also LROC NAC image M1149637354L (16 March 2014).

Impact flash recorded on the unlit Nearside by Prof. Jose M. Madiedo, 11 Sept. 2013. North is to the right (note the visibility of Grimaldi, top center - the 173 km-wide walled plain is often the last recognizable feature on portion of the Nearside lit by Earthshine as the Moon waxes Full). The Moon was shy of First Quarter. This video was produced on the occasion of the publication (in Feb. 2014) in Monthly Notices of the Royal Astronomical Society (MNRAS) of the paper entitled "A large lunar impact blast on 2013 September 11," by J.M. Madiedo, J.L. Ortiz, N. Morales and J. Cabrera-Caño.

A longer, more instructive version was uploaded by the authors HERE. 

Wide Angle Camera morphology basemap overlaid with color-coded LROC GLD100 topography centered on the 11 September 2013 impact crater. The large crater just visible in the lower left is 60 kilometer diameter crater Bullialdus [NASA/GSFC/Arizona State University].

Revisit the LROC NAC image of new crater formed on 17 March 2013, HERE.

Read the paper describing the 11 September 2013 observation (Madiedo et al., 2014)

Secondary scatter over Haret C and the SPA interior

A stream of secondary craters crosses the rim of Haret C (28.47 km; 57.6°S, 186.3°E), stretching from the northeast exterior, southeast into the interior of the crater, deep within the South Pole-Aitken impact basin. 6.52 km-wide field of view from LROC NAC mosaic M1163623161LR, LRO orbit 23388, August 25, 2014; 56.75° incidence, resolution 68 cm from 63.63 km over 57.6°S, 185.26°E [NASA/GSFC/Arizona State University].

H. Meyer

LROC News System

Closely clustered or overlapping craters of similar size and morphology are likely secondary craters.

Secondary craters form when an impactor hits the surface (forming the primary crater) and throws out blocks of material that proceed to form their own craters (secondaries) as they hit the surface.

Sometimes, secondary craters can be difficult to identify if they do not occur in groups. Because craters are used to estimate the age of a surface (a process called crater counting), it is important that scientists are able to identify secondary craters.

Thankfully, in the case of Haret C, the secondary craters stand out from primary craters due to their proximity to each other. Random impacts typically do not form clusters like those draped over Haret C (28.47 km; 57.6°S, 186.3°E) .

A quick look at Haret C made possible by the international burst of lunar exploration briefly inspired by interest in the run-up to the Constellation program. The crater chain is easy enough to see in the medium resolution global albedo mosaic swept up from Chang'e-2. And the basics of the ranges and elevations of the region are displayed using the LROC Quickmap service.

Within high resolution images, smaller craters are used for crater counting. However, secondary craters become more common at smaller diameters introducing a problem for crater counters if the secondaries cannot be distinguished from primary craters. Secondaries counted as primaries result in higher crater counts per unit area, which in turn result in age estimates that are older than the true age of the surface.

Haret C does not dominate, but it is easy to pick out near the center of this HDTV still (larger view HERE) from Japan's lunar orbiter Kaguya (SELENE-1) in 2008. There are two other stills where Haret C and its crater chain are visible in context with central South Pole-Aitken basin and it's larger neighbors Bose (92.5 km; 53.95°S, 190.63°E) and Bhabha (70.52 km; 55.49°S, 194.69°E), HERE and HERE [JAXA/NHK/SELENE].

A key science goal is coming to a better understanding of the morphology or abundance of secondaries relative to primary craters so that more accurate age estimates can be made for smaller, younger terrains: especially important for panning at the scale of the NAC images for future missions to the Moon.

Seven minutes of video from GRAIL-A (Ebb) during orbit 1902 in 2012. Using the student-directed Forward MoonKAM video camera we can close in on the secondary crater chain at Haret C looking north from a perspective beginning at 30 km rising to 41 km over the surface at the end of the sequence. Starting in the polar latitudes of the southern farside the compressed view quickly passes up over the enigmatic interior of South Pole-Aitken basin, over Antoniadi (137.91 km; 69.3°S, 186.94°E, home of the Moon's lowest elevation) north 22° following the meridian that crater shares with Haret C [NASA/JPL/UCSD/SRSC].

Explore the full-width NAC mosaic HERE. Do you see any primary craters in the mix?

Related Posts:

Dark Secondary Craters

Clusters of farside secondaries

Clusters

Crater Chain near Rima T Mayer

Stream of Secondary Craters

Chain of Secondary Craters in Mare Orientale

A Smattering of Self-Secondaries

Lovely Lichtenberg B

Lichtenberg B (4.86 km; 33.253°N, 298.48°) is a beautifully preserved young impact crater. Rock outcrops in the upper portion of the crater wall are due to the successive thin lava flows that filled Oceanus Procellarum more than 3 billion years ago. LROC NAC mosaic M1162852913LR, LRO orbit 23280, August 16, 2014; incidence angle 35.4° at 1.31 meters resolution, from 129.2 km over 32.46°N, 298.45°E [NASA/GSFC/Arizona State University].

H. Meyer

LROC News System

The lack of atmosphere on the Moon can have its benefits. For example, without an atmosphere, there are few processes to degrade landforms.

On Earth, rain and wind are major causes of erosion, but on the Moon, those causes are absent. Erosion on the Moon is due to impacts that cause shaking and can demolish other craters during formation and to gravity pulling material downslope.

In the case of Lichtenberg B, gravity has not yet rendered the crater smooth and subdued, and there are few impacts nearby, much less any that could have affected the morphology of the crater, as Lichtenberg B appears younger than its neighbors.

Extreme close-up of the wall and rim of Lichtenberg B wall and rim, just east of south center, where impact melt flowed and formed a channel, pushing boulders aside in the process. This 430 meter field of view illustrated "Lichtenberg B Flow," released December 2, 2011. LROC NAC observation M120257109R, February 8, 2010 [NASA/GSFC/Arizona State University].

On the downside, the lack of atmosphere means that space weathering is more efficient on the Moon, and fresh, highly reflective crater ejecta darkens over time. Because Lichtenberg B's ejecta deposit is still bright, it is quite young.

Lichtenberg B and about 56 km-field of view of its surroundings shows an ejecta blanket still highly visible, most than half-way through its long process of optical maturity. LROC monochrome (643 nm) observation M120256944CE, LRO orbit 2856, February 8, 2010; 54.76° incidence angle, 57.42 meters resolution, from 40.39 km [NASA/GSFC/Arizona State University].

Crisp morphology and a highly reflective ejecta deposit make Lichtenberg B stand out from many of the nearby impact craters. This exquisitely preserved crater is located to the northwest of Aristarchus Plateau in Oceanus Procellarum, a vast mare unit littered with impact craters and wrinkle ridges. The ejecta deposit is particularly interesting because it displays a wrinkled texture with structures that resemble dunes.

High-angle (late afternoon) incidence view draws some depth of field to the plains impacted by Lichtenberg B. LROC WAC monochrome (604 nm) mosaic of four observations from sequential passes December 8, 2011; 77° incidence, 56.5 meters resolution from 40 km [NASA/GSFC/Arizona State University].

How do these structures form? What makes Lichtenberg B's ejecta deposit different from other craters that lack these dune-like structures? It turns out that Lichtenberg B is not alone. Scientists have observed these same features at Linné Crater and are in the process of determining how they formed.

Forward view (north) from GRAIL-A gravity probe Ebb MoonKAM in May 2012, over northwest central Oceanus Procellarum. The maturing ejecta blanket from Lichtenberg B, Dorsum Scilla and Naumann G are in mid-foreground, with Naumann further beyond, and Naumann B (10.72 km; 37.46°N, 299.3°E) is nearer the horizon. ( MoonKAM image 133655 ) [NASA/JPL/SRSC/UCSD].

Check out the full NAC mosaic HERE.

Related Posts:

Lichtenberg B Flow

On the edge of Lichtenberg

Lichtenberg Crater