Conservational Architecture evaluation and environmental control system based on long-term environmental monitoring data——Taking Guangyuan Qianfoya Cliff Inscriptions Conservational Architecture assessment as an example

The environmental monitoring data of Qianfoya Cliff Inscriptions in Guangyuan, Sichuan Province accumulated since 2014 make it possible to analyze the environmental monitoring data in and out of the Experimental Structure of the Conservational Architecture of Qianfoya Cliff Inscriptions which was built in 2016. By comparing the long-term environmental pattern and differences between the internal and external part of the section, the results indicate that the Conservational Architecture effectively decrease the frequency of short-term sever winds, strong sunshine and extreme high and low temperatures, reduces the short-term temperature and humidity variation range, which creates a stable microenvironment conducive to the preservation of statues without changing the long-term environmental transformation pattern. Moreover, a parameter system for evaluating the conservational architecture, which directly related to environmental damage factors and meets the requirement of measurability and controllability, has been established and control threshold of microenvironment adjustment, which divides abnormal environment state in three levels (caution states, Pre-warning states, Warning states), has been chosen so as to quantitatively evaluate the protection effect of the experimental structure and provide data guidance for daily protection work and environmental control. Based on this parameter system and control thresholds, the total duration of warning states in Qianfoya experimental structure can be reduced by 30% compared with that outside the experimental structure, which further proves that the experimental structure plays a significant role in alleviating the main natural deterioration factors in Qianfoya cliff.

temperature difference on the rock surface is large and the preservation conditions are poor. The temperature, humidity and rock surface temperature of deep caves which are not easily affected by water, sunlight and wind are usually stable.
Deep caves are often well preserved, and extreme temperature and humidity are less likely to occur. However, the overall change trend of temperature and humidity parameters of deep caves and shallow niches is basically consistent and synchronized with the environmental temperature and humidity.
For a single cave, the environmental stability of the inner wall is higher than that of the outer wall, and the east side is higher than that of the west side.
Therefore, it is safe and feasible to simulate the preservation environment of deep caves in niches. Firstly, by comparing the present situation and microenvironment of different caves, it is proved that the preservation environment conditions of deep caves are really beneficial to the preservation, and will not cause sudden environmental changes; Secondly, the preservation condition of the deep cave is a prevailing microenvironment in Qianfoya Cliff area, which makes it technically feasible to approach the preservation condition of the deep cave as close as possible.
Above all, the overall environment of Qianfoya Cliff is stable in temperature and humidity, which is good for preservation.
Proper designed conservation architecture can maintain rock temperature, prevent excessive temperature difference between day and night, reduce extreme high and low humidity, reduce frequent water and salt reciprocating migration and cementation loss on the surface of rocks, and balance the water content at different depths, finally providing a relatively stable environmental preservation state without breaking the thermal, moisture and diffusion balance between stone and the microenvironment,.

Conservational Architecture monitoring result
After the experimental structure of conservation architecture was built up, many years' data, including temperature and humidity, rock surface temperature, wind speed and etc. were compared between the inside and outside of the experimental structure.
Introduction of monitoring sites 138# The cave is relatively deep and located in the upper part of the cliff; The monitoring site is located inside the cave 512# The cave is deep and located in the middle of the cliff; The monitoring site is located inside the cave 431# The niche is very shallow and located in the middle of The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLVI-M-1-2021 28th CIPA Symposium "Great Learning & Digital Emotion", 28 August-1 September 2021, Beijing, China the cliff.
806# The cave is deep and located in the middle of the cliff; The monitoring site is at the front of the south side of the cave, near the entrance.

834
The niche e is very shallow and located in the lower part of the cliff.
535# The cave is deep and located in the the lower part of the cliff; The monitoring site is located inside the cave  The experimental structure has achieved good results in two aspects: wind direction improvement and wind speed control.
Specifically, the average wind speed in a long period of time decreased from 1.26m/s to 0.32m/s, which decreased by three-quarters of the original average wind speed; The wind direction has also been improved from the situation that the north wind dominates and the frequency of the north wind exceeds 30% when there is no experimental structure, to the situation that the wind was diverted to all directions and the frequency of the each directions is about 5-10%.
As far as the regional wind environment is concerned, the experimental structure has played a role in reducing the high wind, stabilizing the wind speed, and diverting the north wind to other directions.   The solar radiation during the daytime does not hit directly on the rock, but first hits on the roof and tile curtain wall of the conservational architecture then conducts heat to the rock through thermal radiation and convection, which actually curbs the direct heating of the rock surface by solar radiation.
Meanwhile, wind speed goes relatively high outside the tile curtain of experimental structure and air between the tiles dissipate heat and carry it away directly by wind, so that the The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLVI-M-1-2021 28th CIPA Symposium "Great Learning & Digital Emotion", 28 August-1 September 2021, Beijing, China temperature inside the tile curtain wall can be cool.
Moreover the temperature on the inner surface of the tiles at night is also much higher than the equivalent temperature of a clear sky, which means that the heat lost by the rock body at night due to the radiation effect will be relatively reduced.
Combining the effects of daytime and nighttime, it can be found that the conservation architecture plays a great role in maintaining the temperature of the rock body and preventing excessive temperature difference between day and night. The average air temperature in the Experimental Structure is essentially the same as in the niches and caves outside, which indicates that the Experimental Structure does not break the basic thermal equilibrium between the artifacts and microenvironment. The maximum temperature within the experimental structure is lower and the minimum temperature is higher than that of shallow niches, and the maximum temperature within the experimental structure is lower and the minimum temperature is higher than that of the deep caves, while the standard deviation and coefficient of variation are similar. This suggests that the experimental structure provides a thermal environment similar to that of deep caves, avoiding extreme high and low temperatures and even more stable. The time-by-time comparison of monitoring data in Figure 3 shows that the thermal environment in the experimental structure is statistically similar to that in deep caves with delayed temperature peaks and smaller temperature fluctuations than that in niches.

Max
The average absolute humidity of the air in the experimental structure is basically the same as that of the niches and caves outside the structure, which indicates that the experimental structure does not break the vapor diffusion equilibrium between the artifacts and environment. The coefficient of variation of absolute humidity in the experimental structures is the smallest and the maximum value of absolute humidity in the experimental structure is moderately low among the monitored caves, indicating that the microenvironment in the experimental structure is relatively dry in the Qianfo Cliff area.

Figure 4
Comparison of relative humidity of microenvironment inside and outside the experimental structure As can be seen in Figure 4, during the daytime when the relative humidity is low, there is basically no difference in the relative humidity of inside and outside the experimental structure; during the rainfall period or at night when the relative humidity is high, the relative humidity inside the experimental structure is significantly lower than that outside the experimental structure. In other words, the experimental structure though has little effect on the minimum value, t reduces the maximum value of relative humidity to a certain extent.
All in all, since the cliff inscriptions suffered less from underground water (Zong, 2011)，there is a great chance to preserve the cliff inscriptions safely by conservational architecture. The microenvironment of caves and niches could be quite different. The shallow niche, which is greatly affected by mountain wind and sunshine, suffers from the large monitoring. In order to ensure the applicability of the evaluation system, the parameters in the system should be classified according to the measurability and controllability of parameters, and at the same time be graded according to the correlation between the parameters and the key damage factors.
Core parameter, which is easy to test and directly related to the deterioration. It includes the temperature of air and the surface of rocks, RH, wind speed, the sun radiation and Air pollutants.

Observation parameter and regular inspection parameter，
which is the phenomenon of environmental change instead of the fundamental factor of environmental change. It cannot be measured directly or is not suitable for frequent measurement.
The observation parameter can generally be converted or extrapolated from the core control indicators; regular inspection parameters are those that are tested every 5-10 years.

Threshold value of the parameter
The core parameters are the main monitoring elements in Due to the data distribution of different parameters, the three-level threshold is divided in different ways according to the actual monitoring situation of each parameter

Temperature
Within a certain period of time, the distribution of temperature monitoring data conforms to the normal distribution. In order to take into account the convenience and accuracy of parameter use, statistics are performed on a monthly basis. Referring to "3σ" mode in statistics, the three-level threshold of temperature can be set as follows: The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLVI-M-1-2021 28th CIPA Symposium "Great Learning & Digital Emotion", 28 August-1 September 2021, Beijing, China  Table 5 The thresholds values of temperature (℃)

Figure 6 RH Distribution
As can be seen from the above graph, the humidity conforms to a skewed distribution, favoring the side of high humidity with a median above 70% and a mode even close to 85%. It can be assumed that there is a prominent risk of degradation by microorganisms under normal conditions. Therefore, combining the "3σ" mode with the actual situation, different threshold determination methods are proposed for the upper and lower thresholds-the lower limits of the humidity threshold follow the same pattern as that of temperature while the upper limit of the humidity thresholds are as follow: Upper limit of normal condition is the value that is repeated most often in the data set.
Upper limit of attention condition is the value at the percentage decided by formula follows: Upper limit of pre-warning condition is the value at the percentage decided by formula follows: Where: M=the mode of RH data (≤ ) =the percentage of the value that is not greater than the mode (> ) =the percentage of the value that is greater than the mode

Wind speed
Wind speed does not show obvious periodicity and regularity in monitoring.
As the overall distribution of wind speed in Qianfoya is similar to the half-normal distribution with static wind frequency as the axis of symmetry. The average wind speed is relatively small, mainly concentrated below 1m/s except for the static wind， but high wind speed occasionally occurred. In view of the distribution characteristics and the randomness of extreme wind speeds, thresholds are as followed: The upper limit of normal conditions is the value not greater than 5% of data; The upper limit of attention conditions is the value not greater than 3% of data. The upper limit of pre-warning conditions is the maximum data.  Table 7 The thresholds values of wind speed (m/s)

ARCHITECTURE
Using the hierarchical parameter system can count the frequency of environmental conditions at all levels, thereby quantitatively describing the effect of the experimental structure and the differences in the microenvironment among caves and niches.   Comparing the monitoring data of environmental humidity, it can be found that the frequency of the humidity data fell in abnormal condition at a monitoring point is generally higher than that of temperature data fell in abnormal condition. showed that the duration of the abnormal condition was longer in the shallow niche while shorter in the deep cave. The total time of the abnormal condition of relative air humidity in caves and niches is also longer than that of the air temperature in caves and niches.

Duration of abnormal conditions of RH /hours
The exceptionally superior humidity environment of shallow caves and niches shows the contradictory relationship between wind speed and environmental humidity: high-speed northwest wind may cause wind erosion to cliff walls, but at the same time air flow is beneficial to divert moisture rapidly to reduce extreme high humidity.
The probability of abnormal conditions in the experimental structure is significantly lower than that of a shallow niche, slightlyl higher than a deep niche, and the distribution ratio of the comparison of the three conditions is consistent with most of caves: the period in Attention conditions is the longest，that in Pre-warning conditions is second, and that in Warning conditions is shortest. It shows that the experimental structure as a whole reduces the frequency of excessively low and excessively high humidity without changing the overall distribution pattern of humidity, and finds a good balance point between air fluidity and environmental humidity. It can be said that the experimental structure has become one of the areas with the best humidity conditions in Qianfoya cliff. There are many other statistical methods of outlier delineation, and this paper only provides an attempt at threshold setting, with much room for refinement. Furthermore, as the monitoring data accumulate, the grading warning model embedded in the monitoring system can be established to improve the graded control threshold system for environmental protection in Qianfo Cliff.