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Communication

Comparative Analysis of Diurnal Thermal Radiation Variation among Lunar Craters of Different Ages Using CE-2 MRM Data

by
Lianghai Wu
1,2,
Zhanchuan Cai
1,*,
Xiu He
1,3,
Yuyun Chen
1 and
Zhiguo Meng
4,5
1
School of Computer Science and Engineering, Macau University of Science and Technology, Macau 999078, China
2
School of Computer Science, Guangdong University of Petrochemical Technology, Maoming 525000, China
3
School of Information and Intelligent Engineering, Guangzhou Xinhua University, Guangzhou(Dongguan) 523133, China
4
College of Geoexploration Science and Technology, Jilin University, Changchun 130012, China
5
State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau 999078, China
*
Author to whom correspondence should be addressed.
Remote Sens. 2023, 15(15), 3857; https://doi.org/10.3390/rs15153857
Submission received: 24 June 2023 / Revised: 30 July 2023 / Accepted: 1 August 2023 / Published: 3 August 2023
Browse Figures
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Abstract

:
Microwave radiometer (MRM) is one of the important payloads on the Chang’e-2 (CE-2) Lunar satellite. In the Chang’e satellite’s observation of the microwave radiation brightness temperature (TB) on the lunar surface, there are some “cold spots” of microwave thermal radiation at night containing the Jackson crater. In order to compare the diurnal radiation TB differences of “cold spots” on the lunar surface, two typical craters at similar latitudes on the northern hemisphere on the lunar farside were selected: Jackson, which represents the new craters with a large number of discrete rocks on their surfaces; and Morse, which no longer has a large number of rocks after long-term meteorite impact and lunar evolution. In this paper, the diurnal variation of CE-2 MRM data in the two craters is presented, and a comparative analysis is made with the (FeO + TiO 2 ) abundance (FTA) obtained by Clementine UV-VIS data and the rock abundance (RA) data of LRO Diviner. We find that the variation of the "cold spots" of lunar surface thermal radiation is closely related to the RA distribution in the newly formed craters on the lunar surface, and also has a certain correlation with the FTA.

1. Introduction

The Chinese Chang’e-1 (CE-1) satellite was launched on 24 October 2007, and successfully completed its data collection mission, returning on 1 March 2009. A state-of-the-art four-channel microwave radiometer (MRM) was deployed aboard the Chang’e-1 spacecraft, with its primary mission focused on acquiring a comprehensive set of global brightness temperature (TB) data, essential for diagnosing the thermal and electrical properties of the lunar surface [1]. In order to improve the accuracy and precision of lunar scientific data, obtain high spatial resolution 3D images of the lunar surface, probe the material composition of the lunar surface layer, and observe the space environment near the Moon and in the lunar orbit, the Chang’e-2 (CE-2) satellite was launched. The CE-2 satellite began its mission on 1 October 2010, and successfully concluded its data collection on 13 December 2012. Aboard the Chang’e-2 spacecraft, an MRM instrument almost identical to the one on CE-1 was deployed, featuring four frequency channels: 3.0, 7.8, 19.35, and 37.0 GHz (corresponding to wavelengths of 10, 3.85, 1.55 cm, and 8 mm, respectively). Importantly, there are some differences between the MRMs on CE-1 and CE-2, including their orbital altitudes. CE-1 operated at an altitude of 200 km above the lunar surface, while CE-2 operated at an altitude of 100 km. Additionally, the antenna footprint of CE-1 MRM covered a distance of 35 km for the 7.8, 19.35, and 37.0 GHz channels, and 50 km for the 3.0 GHz channel. In contrast, the antenna footprint of CE-2 MRM covered a reduced distance of 17.5 km for the 7.8, 19.35, and 37.0 GHz channels, and 25 km for the 3.0 GHz channel [2,3,4]. Therefore, compared to the CE-1 MRM, the CE-2 MRM achieved a more comprehensive coverage of the lunar surface, obtained a greater number of data swath trajectories, and acquired a more exhaustive set of TB data.
Chan et al. used the MRM data of CE-1 to generate TB maps, and obtained interesting lunar surface characteristics from the low-frequency channels that had not been observed before. It is believed that microwave can be used to probe into the heat absorbing layer of the Moon and learn more about the physical characteristics of the surface layer of the Moon [5]. Gong and Jin used CE-1 MRM data to obtain the TB variation distribution of the Sinus Iridum, and analyzed the main factors influencing the physical temperature of the lunar surface [6]. Cai and Lan used CE-2 MRM data to generate a global TB model [7]. Meng et al. studied the thermal radiation characteristics of typical Copernican craters such as Tycho by using the CE-2 MRM data [8,9]. Wu et al. analyzed the characteristics of the King crater using the CE MRM data and discovered new clues related to the formation of anomaly belts around the King crater [10].
In the observation of lunar surface microwave radiation TB by the Chang’e satellites, “cold spots” of microwave radiation have been identified. These cold spots are characterized by lower TB anomalies and are a prominent feature of the Moon during nighttime. The Jackson crater is one of these cold spots. In order to analyze the brightness temperature characteristics of the Jackson crater, another crater, Morse, from a different epoch was selected for comparison. These two craters are typical craters in the northern hemisphere of the lunar far side, with similar latitudes. The Jackson crater represents a new crater with a large amount of scattered rocks on the surface, while the Morse crater has undergone long-term meteorite impacts and lunar evolution and no longer contains significant amounts of rock. The Jackson crater (22.05°N, 163.32°W, diameter: 71.38 km, depth: 2.76 km) is located in the northern part of the South Pole-Aitken Basin, with a high albedo and visible ejecta rays (see Figure 1b,c) [9,11]. It formed during the Copernican period, the youngest geological epoch of the Moon, and continues to the present during the Eratosthenian period, spanning a total of 1.1 billion years. The Morse crater (21.1°N, 175.1°W, diameter: 77 km) is a crater located on the far side of the Moon, at a similar latitude to the Jackson crater (see Figure 1a). It formed during the Eratosthenian period, between 3.2 and 1.1 billion years of the Moon’s geological age, between the Late Imbrian and Copernican periods. It is a relatively well-preserved crater, older than the Jackson crater, and its features have not been significantly eroded by subsequent impacts. Figure 2a shows the geological units in the study area. The rocks on the central peak of the Jackson crater are more dense and larger compared to the rocks on the Morse crater (see Figure 2d,e). Additionally, the Jackson crater represents a new crater with a large amount of scattered rocks on the surface, while the Morse crater no longer contains significant amounts of rock after a long period of meteorite impact and lunar evolution. Therefore, we can analyze the relationship between the rocks and changes in thermal radiation.
To compare the diurnal TB radiation differences of these lunar surface “cold spots”, we conducted several experiments by examining two representative craters at similar latitudes in the northern hemisphere of the lunar farside: the Jackson crater and the Morse crater. This study incorporates CE-2 MRM data, in conjunction with Clementine UV-VIS data and Lunar Reconnaissance Orbiter (LRO) data. It comprehensively investigates the diurnal and nocturnal microwave radiation characteristics, the FTA distribution, and RA distribution of the Jackson and nearby Morse craters, while also analyzing the diurnal variation of surface thermal radiation in this region.

2. Data Processing

2.1. Clementine UV-VIS Data

The United States launched Clementine in 1994, carrying instruments, such as ultraviolet visible camera and near-infrared camera, to obtain multispectral lunar surface reflectance data, which can be used to study the composition of the lunar surface. These data can be obtained from the Lunar Orbital Data Explorer (https://ode.rsl.wustl.edu/moon/index.aspx (accessed on 15 March 2023)). The (FeO + TiO 2 ) abundance (FTA) will directly change the dielectric constant of the medium, and then affect its microwave thermal emission characteristics [14]. Lucey’s method was used to generate the FTA map based on Clementine UV-VIS data [15]. Lucey’s method successfully normalizes the effects of space weathering so that composition may be determined without regard to a surface’s state of maturity, and permit anyone with access to the standard archived DIM to construct high spatial resolution maps of FeO and TiO 2 abundance. Such maps will be of great utility in a variety of lunar geologic studies. Figure 3a,b respectively depict the abundance maps of FeO and TiO 2 . Figure 3c shows that FTA in this area is generally 5–8 wt%, among which the ejecta blanket in the northeast of the Jackson crater is the highest, reaching 10 wt%. However, within the Morse crater, the FTA values are lower, about 4 wt%. Figure 3 shows that the FTA on the crater wall and ejecta blanket is relatively high in the Jackson crater, while the FTA in the northwest of the crater floor is relatively low. In the Morse crater, the FTA of each part is relatively balanced, and the FTA of the crater wall, the central peak and the ejecta blanket is slightly higher than that of other areas.

2.2. LRO Diviner Data

The Lunar Reconnaissance Orbiter (LRO) satellite launched by the United States in 2009, carrying instruments such as the Diviner Lunar Radiometer, can give information about surface and underground temperatures and information about rocks on the surface [16,17]. The lunar surface rocks will directly change the porosity and dielectric constant of the lunar regolith, which is another important factor affecting the microwave thermal radiation of lunar soil [18]. LRO Diviner provides lunar rock debris coverage data, using Bandfield’s algorithm to generate rock abundance (RA) maps for the study area [19].
Figure 4a shows that the Jackson crater has the highest rock abundance, with the RA value higher than 0.4 in some areas. The rocks of the central peak, the wall, and its ejecta blanket are evident. Beyond the Jackson crater, including the Morse crater, the RA value is low, even below 0.01. From the detailed map of the Jackson crater in Figure 4a, it can be clearly seen that the rock blocks are more distributed in the central peak and the western wall. Rock blocks are also more distributed at the junction of the south wall and the crater floor, while the distribution of the east wall and the north wall is relatively small. It can be seen from the detailed map that there are few places with high RA values (red dot positions). For the Morse crater, only the central peak has a sporadic distribution, and the remaining regions are almost non-existent. This is consistent with what is observed from the LROC NAC ROI Mosaics high-resolution image.
We downloaded Diviner Channel 8 nighttime data from the PDS Geosciences Node website (https://pds-geosciences.wustl.edu/ (accessed on 15 March 2023)) to generate infrared TB map of the study area. Figure 4b shows that in the Jackson region, at night, the TB is different from that of the surrounding area, and the infrared TB is larger than that of the surrounding area. Figure 4b also shows that the infrared TB of the Jackson crater and its ejecta blanket is higher, and the infrared TB of the west wall, the central peak and the east wall is the highest, reaching above 140 K. Due to the lack of data on the north wall and the south wall, the actual situation cannot be seen. However, on the whole, the infrared TB of the Jackson crater is higher than that of regions at the same latitude. Clearly, the Jackson crater is an infrared “hot region”. For Morse, there is no characteristic of high TB. In the Morse crater, we can see that in this area, the infrared TB values are similar but basically we can see that the infrared TB values in the southwest and northeast directions are slightly higher, while those in other places are lower.

2.3. MRM Data Processing and TB Related Maps

China launched lunar exploration satellite CE-2 in 2010. The MRM is one of the payloads on CE-2 [7,20,21]. The microwave radiometer has four channels with frequencies of 3.0, 7.8, 19.35, and 37.0 GHz. The main task of the microwave radiometer is to measure the TB of the Moon surface [13,22,23].
During its 7-month operation in the lunar orbit, the CE-2 MRM obtained approximately 8.7 million measurements. Each measurement had a spatial resolution of approximately 25 km at 3 GHz and approximately 17.5 km at 7.8, 19.35, and 37 GHz. The time interval between each record was 1.6 s, during which the satellite covered approximately 2.6 km, resulting in a high degree of trajectory overlap. Adhering to the PDS3 data standard, all TB data were meticulously archived, distributed across 2401 files, with each file corresponding to one orbit. In this study, we utilized MRM 2C-level data, which had undergone meticulous systematic and geometric calibration. These files were made publicly available through the China Lunar Exploration Project Data Release and Information Service System. MRM data include longitude, latitude, observation time, four-frequency TB data, solar incidence angle, azimuth, and data quality. After hour-angle processing, the TB values of lunar daytime and nighttime analysis are obtained [2].
For the calibration issue of the CE-2 MRM data, it was widely reported by Feng et al. [24], Hu and Keihm [25], Hu et al. [26], and Siegler et al. [27]. Advantageously, in the comparative aspect, the MRM data show good correspondence with the lunar surface materials in the global scale, which was thoroughly evaluated by Chan et al. [5], Zheng et al. [1], Cai and Lan [7], Zhu et al. [4], Feng et al. [24], Siegler et al. [27], and Wei et al. [28]. Even on the local scale, the great correlation between the basaltic units and the TB performance results was verified in the Maria Imbrium, Moscoviense, and Rumker regions [21,29]. Thus, though there exists a global calibration issue for the CE-2 MRM data, it has a negligible role in our understanding of the special TB behaviors and the ththermophysical features of the regolith over the lunar surface.
In the absence of water on the Moon, microwaves can penetrate the lunar regolith 10 to 20 times longer than wavelengths [21,30,31]. Table 1 shows that at 3.0 GHz, the penetration depth of microwaves in the lunar regolith can reach 100–200 cm, while at 37.0 GHz, the penetration depth is only 8.1–16.2 cm. The penetration depth of low frequency is greater than that of high frequency. Therefore, the composition of the lunar regolith can be known from the MRM data at different frequencies.
Approximately 1 point in the horizontal direction and 9 to 10 points in the vertical direction in each degree make up the original MRM data points, which are relatively few (see Figure 5). Through comparative analysis, the data at 1 o’clock and 13 o’clock of lunar local time have fewer anomalous bands and better effects, so these two periods are used to represent the TB at midnight and midday. In our research area, there are no MRM data available at 0 and 2 o’clock, so we use the data from 1 o’clock instead. There are 520,454 points at 1 o’clock and 2790 points within the study area. Taking 37.0 GHz data as an example, their distribution is shown in Figure 5a. There are two directions in the data at 1 o’clock. In our experiment, if we use the data from two directions at the same time, the plot comes out very poorly as shown in the following Figure 6. The presence of anomalous bands with eastward tilted distribution is visible in the figure. Combined with its distribution characteristics, 1370 data points in the northeast direction were removed from our calculation in order to reduce the calculation workload and avoid errors or interference, and the distribution diagram of the remaining 1420 data is shown in Figure 5b.
The TB map was generated from CE-2 MRM data in the following steps [23,32,33]: Firstly, the measured TB data were binned into a 24-h interval by incorporating the hour angle. While the footprint size of the CE-2 MRM instrument at 3.0 GHz was approximately 25 km, and around 17.5 km for other channels, the selected MRM data points were projected onto the WAC image along the longitude with high original spatial resolution, approximately 1-degree resolution along the latitude. Secondly, there was minimal variation in TB values along the latitude. Then, the obtained discrete point data had to be interpolated in order to produce continuous microwave TB maps. Therefore, the ordinary Kriging method was used for interpolation [34]. The TB distribution maps at the resolution of 0.125° × 0.125° (8 pixels/degree) at midnight and midday were generated. Figure 7 and Figure 8 represent midnight and midday TB maps overlaying the geologic map respectively. Figure 9 shows the distribution of the difference between midday and midnight, which is the TB difference. These two time periods proved suitable for investigating the thermal properties of weathered layers containing rocks [35]. Finally, we combine these maps and other data maps to analyze the thermal radiation characteristics of the study region.

3. Microwave Thermal Emission Features

3.1. TB at Midday

Figure 7 shows the midday TB of the study area, indicating that there are obvious thermal anomalies around the northern wall of the Jackson crater, which form a ring shape with the thermal anomalies of the south outer wall. This thermal anomaly ring is particularly noticeable in the 19.35 and 37.0 GHz maps. From the figures, the TB of the Jackson crater’s north inner wall and south outer wall is higher than that of the crater floor and the periphery of the ejecta blanket. Inside the crater, the northern wall has the highest TB, followed by the eastern and western walls, and the southern wall and the crater floor have the lowest TB. The map of 3.0 GHz is slightly different from the other three channels, but locally, its rule is basically consistent. For the Morse crater, the TB of the north inner wall and south outer wall is also higher than for other regions, but the TB difference in different regions is small, so it is not obvious in a large range of regions with a larger TB threshold.
In the southeastern direction of the Jackson crater, there are also two small hot anomalous craters (19–20°N, (−162)–(−160)°W). These two small craters have higher TB values than the surrounding area, especially at 7.8 GHz and 19.35 GHz channels. In contrast, in the northwestern direction of the Jackson crater, there are also two small cold anomalous craters (20–24°N, (−170)–(−165)°W), which are particularly noticeable for the 7.8 GHz and 19.35 GHz channels. In the northwestern direction (22–25°N, (−180)–(−167)°W) and northeastern direction (22–24°N, (−175)–(−172)°W) of the Morse crater, there are also small cold anomalous craters present.

3.2. TB at Midnight

Figure 8 shows the midnight TB maps at different frequencies of the study area. On the whole, the Jackson crater has a strong cold anomaly, and its TB is significantly lower than its surroundings, which is typical of microwave “cold spots”. The TB values of the Jackson crater and its ejecta blanket are lower than those of surrounding areas. The southwestern portion of the crater floor has the lowest TB. The TB slowly increases in the direction of the ejecta blanket. The TB of each channel is not the same because different channels of microwave penetrate the Moon surface at different depths. In the 3.0 GHz channel, the area where the Jackson crater TB is low is larger, and the TB values of the impact crater and the north ejecta blanket are low. On the other hand, in the 37.0 GHz channel, the region where the TB is at the cold value is relatively small, but it increases slowly from the impact crater, which can be seen sputtering to the periphery of the impact crater. For the Morse crater, there are no obvious anomalies. Only the TB distributed of the south wall in the low frequency 3.0 GHz and 7.8 GHz channels is slightly lower than that of the surrounding area, but the difference is not too large, at about 3–5 K. The TB of the remaining areas in the Morse crater is similar to that of their surroundings.

3.3. TB Difference

Figure 9 shows the TB difference distribution between midday and midnight at different frequencies. The TB difference of the central peak of the Jackson crater is the largest, and the difference from the central peak to the outside gradually decreases. The area with the large TB difference basically corresponds to the Jackson crater. The TB difference outside the ejecta blanket in the crater decreases to a lower level. In the 37.0 GHz TB distribution, the TB difference outside the ejecta blanket is somewhat different from the distribution characteristics of 19.35 and 7.8 GHz. When it expands outward, it becomes smaller and has a larger coverage. For the TB distribution of the Morse crater, the distribution of 3.0 GHz is inconsistent with that of the other three frequencies. The brightness temperature difference in the northwest and southeast of the crater is higher, but at 3.0 GHz, the TB value at the bottom of the impact crater is only slightly lower than that in the northwest and southeast. Overall, with the increase in frequency, the value of TB difference also increases, from over 9 K at 3.0 GHz to about 90 K at 37.0 GHz.

4. Result and Discussion

4.1. Comparison of TB Diurnal Variation

Figure 10 shows the variation of the TB average of Jackson and Morse craters. At the lunar day, as the sun rises, the TB of the Jackson and Morse craters rises quickly, reaches its peak at around 14:00, and then falls quickly. In the lunar night, however, the TB drops steadily, reaching its lowest point just before sunrise. The high-frequency TB curves of 19.35 GHz and 37.0 GHz reveal that there is a great difference in the rising and falling rates of TB at different times of the lunar day. The TB increases rapidly from 6:00 to 14:00, decreases rapidly from 14:00 to 18:00, and decreases slightly from 18:00 to 6:00.
Figure 10 shows that the average TB of the Jackson crater is larger than that of Morse. The largest TB change is 37.0 GHz. In the Jackson crater, the difference between the maximum and minimum values is higher than 120 K, while in the Morse crater, the difference is also higher than 80 K. The frequency with the smallest TB variation is 3.0 GHz. In the Jackson crater, the difference between the maximum and minimum values is about 45 K, while in the Morse crater, the difference is about 20 K. Table 2 shows that among all channels, the average TB of the Jackson crater at night is lower than that of the Morse crater, while the TB average of the Jackson crater is higher than that of the Morse crater. Obviously, from Figure 10 and Table 2, the TB variation of increases with the increase in frequency. Figure 10 also shows that the low TB appears around 5 o’clock, and the high value appears around 14 o’clock, which is consistent with the Tycho and Maurolycus craters study of Gong et al. [36].

4.2. Hot TB Anomaly

Figure 7b–d show obvious thermal anomalies at midday in the Jackson crater. Gong and Jin pointed out that the microwave thermal anomaly of the new impact crater is mainly related to rock blocks [6]. In the newborn impact crater Jackson, there are also obvious rock blocks (see Figure 4b). However, it does not completely conform to this law. Combined with Figure 4b and Figure 7, it is found that the location of the highest TB is not consistent with the distribution of the rock blocks, which are mainly concentrated at the floor, while the locations of high TB are mainly the northern wall and the southern outer wall. In the case of the Morse crater, high TB also occurs on the north walls and south outer walls, and there are no visible rocks at the floor of the crater. This phenomenon indicates that the hot TB anomaly is related to solar radiation and topography, which is consistent with the study of Meng et al. in the Tycho crater [8].
However, Figure 10 and Table 2 show that the average midday TB of the Jackson crater is higher than that of the Morse crater at 37.0 GHz and 19.35 GHz. At low frequencies, the average midday TB of the Jackson crater is similar to that of the Morse crater. This requires further exploration of the relevant reasons, which will be discussed at the later section.

4.3. Cold TB Anomaly

Figure 8 shows an obvious cold anomaly in the Jackson crater at midnight. It is found that the lowest TB is located in the crater floor. Combined with Figure 4a,b and Figure 8, most of the low TB is related to FTA and RA.
As can be seen in Figure 8, the Jackson crater is a cold spot. At each frequency, the TB of the crater is obviously lower than that of its surrounding area. The southwest region of the impact crater is the lowest TB, and the TB increases gradually from this point to the outside of the spatter blanket. In the 37.0 GHz figure, it can be seen that the TB change on the outside of the crater bursts out in a star shape. This is basically consistent with the direction of the splash rays in Figure 1b.
The radiation pattern of the impact crater also has different degrees of TB anomalies. The TB of the Moon decreases gradually from the center of the cold spot at noon, and increases gradually from the center of the cold point at night.
For the Morse crater, it can be seen that the lowest TB is located in the southern inner wall, but there is no obvious anomaly in other regions.

4.4. Cause Analysis

The TB in the Jackson crater is much colder than that around it at night, while the TB in the Morse crater is higher than that around it at noon. This phenomenon of cold spots at night and hot regions during the day is consistent with the description of the newer crater characteristics in Chan et al.’s work [5]. Figure 9 shows the TB difference between midday and midnight in this area. The TB difference in the Jackson crater area is the highest and gradually decreases outward, especially at high frequencies. Meng et al. suggested that the difference at the same frequency could eliminate the influence of the surface environment [8].
Table 3 shows the correlation coefficients between the TB difference at 19.35/37.0 GHz and RA/FTA. It can be seen that for the correlation coefficient between the TB difference and RA, there is a strong positive correlation between the TB difference and RA in the Jackson crater, while there is a weak negative correlation between the TB difference and RA in the Morse crater. The statistical results are consistent with the direct observations from Figure 4a and Figure 9. Because the imaginary part of the rock’s dielectric constant is large and the penetration depth of the microwave is small, the rocks can shield the thermal radiation of the lower lunar soil, which increases the diurnal variation of microwave radiation in the Jackson and other newly formed craters. Older craters, such as Morse, have little diurnal variation in microwave thermal radiation due to the absence of rocks [6].
In Figure 3a, the FTA on the crater wall and ejecta blanket is relatively high for the Jackson crater, while the FTA in the northwest of the crater floor is relatively low. In Figure 8a, the TB values around the Jackson crater are particularly small at 3 GHz, but at other frequencies, the TB values around the Jackson crater gradually increase with increasing frequency, and a thermal anomaly appears. Thus, in the Jackson crater, TB differences are moderately positively correlated with FTA, and the correlation changes from negative to positive with increasing frequency. In the Morse crater, the FTA is relatively balanced in all parts, but the TB is higher in the north inner wall and south outer wall. Hence, in the Morse crater, the TB differences are weakly correlated with FTA. Since the Jackson crater has a large number of new craters with discrete rocks on its surface, the Morse crater no longer has a large number of rocks after a long period of meteorite impacts and lunar evolution. Therefore, there is a correlation between the meteorite content and TB values. In the TB difference at high frequency, the ejecta blanket and sputter ray outward with the Jackson crater as the center are consistent with the star-shaped sputter rays observed in Figure 1b, and also coincide with the FTA distribution in Figure 3c. Combined with the correlation coefficient between the FTA and TB difference, we believe that FTA is another factor affecting TB variation of this region.
Moreover, in the TB difference at high frequency, the ejecta blanket and sputter ray, which are outward with the Jackson crater as the center, are consistent with the star-shaped sputter rays observed in Figure 1b, and also coincide with the FTA distribution in Figure 3a. Combined with the correlation coefficient between the FTA and TB difference, we believe that FTA is another factor affecting TB variation of the study region.
In conclusion, RA is the main reason for the diurnal TB variation of the newborn impact crater Jackson, while FTA is another factor for the TB variation in this region, especially in the sputtering area outside the crater.

4.5. Analysis and Summary

(1) We present the daily variations of the CE-2 MRM data for two craters, and analyze them in comparison with the (FeO + TiO 2 ) abundance (FTA) from the Clementine UV-VIS data and the rock abundance (RA) data from the LRO Diviner. We find that the variation of the “cold spots” of thermal radiation on the lunar surface is closely related to the RA distribution of newly formed craters on the lunar surface, and has some correlation with the FTA.
(2) The diurnal and seasonal characteristics of microwave radiation, along with the FTA and RA distributions of the Jackson and nearby Morse impact craters, were investigated to analyze the diurnal variation patterns of surface thermal radiation in this region. In the Jackson impact crater, the noon TB data revealed a significant thermal anomaly around the northern wall, forming a ring-like pattern in conjunction with the thermal anomaly on the outer southern wall. Within the same region, different frequency midnight TB maps unveiled a strong cold anomaly within the Jackson impact crater, where TB values were notably lower than the surrounding environment, resembling a typical microwave “cold spot”. As for the Morse impact crater, no significant anomalies were observed, except for a slightly lower TB distribution on the southern wall at the lower frequencies of 3.0 GHz and 7.8 GHz, with the differences being minor, approximately 3 to 5 K. In the surrounding area of the Morse impact crater, TB values were similar to the surrounding environment. The distribution of differences between noon and midnight TB values at different frequencies exhibited an increasing trend with frequency, with the TB difference rising from over 9 K at 3.0 GHz to around 90 K at 37.0 GHz.

5. Conclusions

Based on CE-2 MRM data, the midnight and midday TB of the Jackson crater and the adjacent Morse crater were analyzed. By combining this analysis with the TB variation curve, RA, FTA, and microwave radiation characteristics were discussed. The results demonstrated that the variation of microwave thermal radiation is more pronounced in the newly formed Jackson crater compared to the older Morse crater. It is suggested that (1) the TB diurnal variation in the Jackson crater is primarily caused by RA distribution, and (2) in this region, FTA also plays a substantial role in the variation of TB, particularly in the ejecta area outside the Jackson crater and its star-shaped sputtering rays.

Author Contributions

Conceptualization, L.W. and Z.C.; methodology, L.W.; software, L.W. and Y.C.; validation, Z.M.; formal analysis, Z.C. and X.H.; investigation, Y.C.; resources, Z.C.; data curation, L.W. and Y.C.; writing—original draft preparation, L.W.; writing—review and editing, L.W. and Z.C.; visualization, L.W.; supervision, Z.C.; project administration, Z.C.; funding acquisition, Z.C. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported in part by the Science and Technology Development Fund of Macau under Grants (0059/2020/A2, 0052/2020/AFJ, 0025/2019/AKP).

Acknowledgments

We thank the Lunar and Deep Space Exploration Science And Application Center, National Astronomical Observatories, Chinese Academy of Sciences, for providing us with the lunar maps and relevant data. We also acknowledge the use of imagery from Lunar QuickMap (https://quickmap.lroc.asu.edu (accessed on 15 April 2023)), a collaboration between NASA, Arizona State University & Applied Coherent Technology Corp. Furthermore we would like to express our gratitude to the reviewers for their valuable feedback and constructive suggestions.

Conflicts of Interest

The authors declare no conflict of interest regarding the publication of this paper.

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Figure 1. (a) Morse crater LROC NAC ROI Mosaics (https://bit.ly/3zr4Azk (accessed on 6 April 2023), is from QuickMap website). (b) Digital orthophoto of CE-1 on the far side of the Moon (http://moon.bao.ac.cn (accessed on 6 April 2023)), (c) Jackson crater LROC NAC ROI Mosaics (https://bit.ly/3vcuJiO (accessed on 6 April 2023), is from QuickMap website). (d) The center peak of Morse crater (https://bit.ly/3VDlQZV (accessed on 6 April 2023)). (e) The center peak of Jackson crater (https://bit.ly/3GwkMCK (accessed on 6 April 2023)).
Figure 1. (a) Morse crater LROC NAC ROI Mosaics (https://bit.ly/3zr4Azk (accessed on 6 April 2023), is from QuickMap website). (b) Digital orthophoto of CE-1 on the far side of the Moon (http://moon.bao.ac.cn (accessed on 6 April 2023)), (c) Jackson crater LROC NAC ROI Mosaics (https://bit.ly/3vcuJiO (accessed on 6 April 2023), is from QuickMap website). (d) The center peak of Morse crater (https://bit.ly/3VDlQZV (accessed on 6 April 2023)). (e) The center peak of Jackson crater (https://bit.ly/3GwkMCK (accessed on 6 April 2023)).
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Figure 2. (a) Geologic map of the study area. Cc—Copernican Crater; Ec—Erastosthenian Crater [12]. (b) Topography of the study area [13], covered with the geologic map.
Figure 2. (a) Geologic map of the study area. Cc—Copernican Crater; Ec—Erastosthenian Crater [12]. (b) Topography of the study area [13], covered with the geologic map.
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Figure 3. (a) FeO map, (b) TiO 2 , and (c) FTA map based on Clementine UV-VIS data, the FTA map covered with the geologic map.
Figure 3. (a) FeO map, (b) TiO 2 , and (c) FTA map based on Clementine UV-VIS data, the FTA map covered with the geologic map.
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Figure 4. (a) Rock abundance map based on lunar rock data from LRO Diviner, and (b) infrared thermal emission observed from LRO Diviner Channel 8 at night, covered with the geologic map.
Figure 4. (a) Rock abundance map based on lunar rock data from LRO Diviner, and (b) infrared thermal emission observed from LRO Diviner Channel 8 at night, covered with the geologic map.
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Figure 5. Scatter plots of the study area with the frequency of 37.0 GHz at midnight, (a) 2790 points and (b) 1420 points.
Figure 5. Scatter plots of the study area with the frequency of 37.0 GHz at midnight, (a) 2790 points and (b) 1420 points.
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Figure 6. TB plot generated by 1 o’clock band interference data.
Figure 6. TB plot generated by 1 o’clock band interference data.
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Figure 7. TB maps covered with the geologic map at midday: (a) 3.0 GHz, (b) 7.8 GHz, (c) 19.35 GHz and (d) 37.0 GHz.
Figure 7. TB maps covered with the geologic map at midday: (a) 3.0 GHz, (b) 7.8 GHz, (c) 19.35 GHz and (d) 37.0 GHz.
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Figure 8. TB maps covered with the geologic map at midnight: (a) 3.0 GHz, (b) 7.8 GHz, (c) 19.35 GHz and (d) 37.0 GHz.
Figure 8. TB maps covered with the geologic map at midnight: (a) 3.0 GHz, (b) 7.8 GHz, (c) 19.35 GHz and (d) 37.0 GHz.
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Figure 9. TB difference maps covered with the geologic map: (a) 3.0 GH, (b) 7.8 GHz, (c) 19.35 GHz and (d) 37.0 GHz.
Figure 9. TB difference maps covered with the geologic map: (a) 3.0 GH, (b) 7.8 GHz, (c) 19.35 GHz and (d) 37.0 GHz.
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Figure 10. TB variations of Morse and Jackson craters, the time points without original data (0:00, 2:00, 5:00, 7:00, 9:00, 11:00, 15:00, 18:00, and 20:00) were averaged before and after.
Figure 10. TB variations of Morse and Jackson craters, the time points without original data (0:00, 2:00, 5:00, 7:00, 9:00, 11:00, 15:00, 18:00, and 20:00) were averaged before and after.
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Table 1. Penetration depth of microwave on lunar regolith.
Table 1. Penetration depth of microwave on lunar regolith.
FrequencyWavelengthPenetration Depth
3.0 GHz10 cm100–200 cm
7.8 GHz3.85 cm38.5–75 cm
19.35 GHz1.55 cm15.5–31 cm
37.0 GHz0.81cm8.1–16.2 cm
Table 2. Average TB values of the craters.
Table 2. Average TB values of the craters.
TimeCrater3.0 GHz7.8 GHz19.35 GHz37.0 GHz
MidnightMorse222.82211.89220.70204.70
MidnightJackson216.99204.76210.19192.72
MiddayMorse227.04222.30253.22272.15
MiddayJackson223.90224.32259.40278.69
Table 3. Correlation coefficients between RA/FTA and TB difference.
Table 3. Correlation coefficients between RA/FTA and TB difference.
CraterItem19.35 GHz37.0 GHz
MorseRA−0.18585−0.19021
MorseFTA0.256720.274681
JacksonRA0.7225910.658989
JacksonFTA0.5162730.438769
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Wu, L.; Cai, Z.; He, X.; Chen, Y.; Meng, Z. Comparative Analysis of Diurnal Thermal Radiation Variation among Lunar Craters of Different Ages Using CE-2 MRM Data. Remote Sens. 2023, 15, 3857. https://doi.org/10.3390/rs15153857

AMA Style

Wu L, Cai Z, He X, Chen Y, Meng Z. Comparative Analysis of Diurnal Thermal Radiation Variation among Lunar Craters of Different Ages Using CE-2 MRM Data. Remote Sensing. 2023; 15(15):3857. https://doi.org/10.3390/rs15153857

Chicago/Turabian Style

Wu, Lianghai, Zhanchuan Cai, Xiu He, Yuyun Chen, and Zhiguo Meng. 2023. "Comparative Analysis of Diurnal Thermal Radiation Variation among Lunar Craters of Different Ages Using CE-2 MRM Data" Remote Sensing 15, no. 15: 3857. https://doi.org/10.3390/rs15153857

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