Mapping Decomposition: A Preliminary Study of Non-Destructive Detection of Simulated body Fluids in the Shallow Subsurface

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Review of “Mapping decomposition: non-destructive detection of simulated body fluids in the shallow subsurface.”

 The authors have made some minor amendments to the paper, but the main concerns remain.

 The issues with the paper as submitted are as follows

 1 Inadequate methodology and design of the experimental work.

 2 Inadequate quantification of the soil parameters.

 3 Inadequate signal processing and assessment of the results.

The design of the experiment consisted of digging a pit 0.5m by 0.5m by 0.5m deep to simulate 25% of a human. In reality, graves are larger and rectangular in shape. The decomposition of a body, pooling and leaching of body fluids into the sub soils depends on the mechanics of the soil as well, its composition as well as the layout of the grave. It is well known that soils such as clay and peat which inhibit the decay process can aid the retention of burial features for centuries. Their mechanical transport mechanisms are radically different.

The authors fail to discuss these issues which are significantly important in terms of the migration of simulated body fluids into the subsoil. The water content of the soil, the water table are all factors which influence transport yet there is little consideration of these. The soil density and composition in terms of sand silt and clay should have been measured. Techniques such as the cone penetrometer for determining the soil density should have been used and reported

The authors stated values at 500 MHz for permittivity and average conductivity for the soil based on a literature survey. This may or may not be relevant to the soil at the site, which was used, and the lack of in-situ measurement is unacceptable experimental technique.

The values of electrical soil propagation parameters both over the range 200 MHz to 2 GHz should have been taken and recorded at the time of the experiment. The square sided hole creates radar corner reflectors and is poor experimental design as it gives rise to unwanted reflections. It is well known that excavated soil requires careful compaction and enough time to settle to avoid spurious GPR reflections. Often a week should elapse before measurements are taken yet the paper reports results taken within the first few days. These may be of doubtful value.

The data images provided show little evidence of migration in contrast to the claimed application of standard DME. The hyperbolic patterns appearing in the data are evidence of lack of proper migration. Figs 3 to 7 are annotated with zones indicating the area of interest, but these obscure the actual data.

Examining these areas carefully does not reveal much evidence of a shift in range of any strong reflector which should be the case if a return from the saline solution gradually shifts downwards due to gravity. In fact, it is difficult to spot such differences as the data in fig 7 and fig 3 also show significant differences which without a-priori knowledge would make identification of such a saline zone difficult. A set of images showing deltas from image to image in range returns as a function of time would have been more convincing

The paper lacks careful analysis of the transport of saline zones through the soil as a function of time or soil property, lacks careful analysis of the GPR data, any simulation of expected returns, lacks scientific rigour and is unconvincing. It does not increase the understanding of the situation and is unsuitable for publication.

 

 

 

Author Response

Thank you for your comments.

The true nature of a scientific experiment, especially one that has never been tried, is precisely to test the validity of the preliminary steps without including too many independent variables in the equation. The purpose of this preliminary scientific experiment was precisely to have a simple and basic starting point and then to be able to make modifications and add variables to make it more complex and at the same time equally robust. If I had included a number of variables from the outset, they would have led to results that were difficult to interpret. Instead, by starting with a simple, basic problem and demonstrating its effectiveness, we are ready to undertake more and more gradually complex experiments (which we are already doing). The objections raised can be supported, but if we deal with this experiment at an advanced stage. Here we are proposing a preliminary experiment that cannot lead to subsequent more complex steps unless we start from simple situations with a few controlled variables. Simplifying an experiment as a starting point for subsequent deepening and complications is not synonymous with a superficial and inadequate experiment. On the contrary, it is precisely the starting point for more in-depth future research.
Consequently, this is the reason for having used a smaller burial (in my decades of experience at crime scenes worldwide, I am aware of dozens of different shapes, sizes and types of burials, but here an attempt was made to simplify for the reason explained above). Also the dynamics of body fluid migration and the ability of different soils to interfere with the decay process are obviously variables that need to be studied and explored in subsequent experiments but cannot be dealt with all at once unless we proceed by different, progressively more complicated steps.
Moreover, let always remember that we are in a forensic context that must be valid worldwide and not all law enforcement agencies have unlimited capabilities, tools and support at their disposal. Gradual approaches that bring out the potential of mostly rapid and non-invasive analyses are easy to apply even in difficult scenarios and contexts.
Coming to the discussion of some technical aspects, it is argued that permittivity and average conductivity for the soil have been estimated from the literature. This is absolutely not true and if one read more carefully it is possible to see that the estimation of the average dielectric constant is 7 based on hyperbola calibration. Furthermore, excavation-related edge effects are obviously part of the experiment since, as is well known in forensic and archaeological GPR, it is precisely the excavation limits that aid in the correct interpretation of the GPR data. Finally, the GPR data was migrated according to the DME standard as repeatedly stated.

Reviewer 2 Report (Previous Reviewer 1)

The authors have done a conscientious and thorough job of addressing the reviews. It is suggested to consider the publication of the manuscript.

 

 

 

Author Response

Thank you for your comment.

Reviewer 3 Report (New Reviewer)

This paper presents a preliminary experiment studying the fluid dispersion in the subsurface using simulated body fluids in a shallow grave and detecting it through the GPR technique and other remote sensing techniques.

The experiment aimed to find and investigate geoscientific methods that are non-destructive to the crime scene and establish how they can assist a criminal investigation and help law enforcement to map and locate suspicious burials.

The authors discussed the limitations and perspectives of their proposed technique.

The paper bnrings a novel approach that needs more assessments and experiments. RS can bring a lot of help to crime scence investigator.

1. Title:

you need to mention that is a preliminary study.

2. Abstract: 

some of the main results should figure in the abstract.

3. Introduction:

- you have well introduced the topic of your experiment.

- avoid the use of long sentences.

4. Material and Methods: 

well detailed.

5. Results and Discussion:

- What about carbonized bodies? mass graves? Burried bodies wearing clothes? you need to discuss these alternative.

- The results of GPR, NDVI, and VARI could be summarized in a table the facilitate the reading.

- When discussing the limitation of the experiment, i think you need to mention that somes graves could be modified by animals that dig for the body.

6- Conclusions:

- line 443: you need to correct the sentence or devide it.

 

 

 

Author Response

Thank you for you useful comments, we have addressed all of them. Please, see the details below:

1. Title:

We have mentioned that is a preliminary study.

2. Abstract: 

Some of the main results were illustarted in the abstract.

3. Introduction:

We removed long sentences.

4. Results and Discussion:

- We have discussed carbonized bodies, mass graves, buried bodies wearing clothes as well.

-  We have summarised the results of GPR, NDVI, and VARI  in a table to facilitate the reading.

- We have mentioned scavengers actions.

6- Conclusions:

- We have corrected it.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

It is suggested to consider the publication of the manuscript.

Author Response

Thank you very much for your time and effort in reviewing our work. We really appreciated it.

Reviewer 2 Report

The paper presents an experimental study on the detection of subsurface simulated body fluids using GPR. The methodologies are well described and the results are solid. The reviewer has the following suggestions. 

As GPR receives reflected signals based on the contrast of relative permittivity of the target and its surrounding environment, the relative permittivity of the surrounding soil of the body fluids should be presented.

In addition, different weather can cause changes in soil properties. For example, rainfall increases soil moisture, and thus results in higher relative permittivity and conductivity of the soil. How did weather conditions affect the detection results?

Author Response

Thank you very much for the time and effort spent in reviewing our paper and thank you for the valuable comments on our work. The data on the dielectric constant of the soil before the ingression of the simulated body fluid has been added.
Although the weather during the 36 days had been mostly rainfall-free, due to the nature of this initial experiment, we chose not to take into account the influence of rain. This will be taken into account when conducting a future, larger-scale experiment.

Reviewer 3 Report

An interesting experiment but lacks rigour, scope and breadth. The chief concern is the failure to adequately describe the transport mechanisms of body fluid flows in soil. Only one type of soil has been considered and even then the characteristics of the soil in terms of the proportions of silt, clay, vegetable matter and sand are not stated. Migration of body fluids in soils evidently depends on the physical transport permeability of the soil and for GPR the difference between the soil complex impedance and the complex impedance of body fluid zone. In a clay soil this may be clearly defined whereas in a sandy soil the zone will rapidly migrate and may not show a clear boundary. No information as to the relative reflection coefficients of such zones is offered and how they would change with time and situation. The paper deals with a very limited case and does significantly add much knowledge. A major improvement to the paper involving considerably more theorectical and practical work is needed as far as the GPR experiments are concerned.

Author Response

Thank you very much for your time and effort in reviewing our work and providing helpful comments. We are aware of the biased nature of this experiment that has been designated as initial and preliminary. This aspect obviously led us to focus on only one soil type to better understand how to proceed in the future with wider-ranging experiments that take into account not only the different soil components but also other inherent characteristics. Therefore, we have emphasized more in the text how this is a preliminary experiment to test the validity of this approach with few variables. Later the variables will increase and all will be duly considered and studied.

Round 2

Reviewer 3 Report

The revised paper does not adequately address the deficiencies noted in the first review and does not increase the understanding of the phenomena