# Systematic Mapping Study on Remote Sensing in Agriculture
## 2 Research Methodology
### Data Extraction Strategy  
The data extraction strategy refers to the way in which each question should be answered for each selected paper. This step requires a previous classification of the possible answers to each MQ and some indications to extract this information from the papers. The extraction strategy developed for the present study was as follows. * **MQ1**. To answer this question, the publication source and channel for each paper should be identified. The channel can be classified in journals, books, and conferences. The source refers to the name of the corresponding journal, book, or conference. * **MQ2**. In order to draw conclusions about the publication trends, articles should be classified per publication year. Therefore, this question extracts the year of each paper. * **MQ3**. Research works can be of different types, for example, a paper can propose new methods and techniques, it can evaluate existing solutions in a new application, or it can describe a specific experience that could be useful for other researchers. According to the authors of [88], the types of research can be classified into the following categories. * Evaluation Research. In this case, the research consists of the evaluation of an approach in RSA. This class also includes identifying new problems in RSA. * Solution Proposal. Research works which involve proposing a new solution for an existing problem in RSA. The proposed approach must be new, or it can be relevant modification of some existing method. An extensive experimentation is not required. * Experience Papers. These articles describe the personal experience of the authors. The paper explains what has been done and how it has been done in practice, and the obtained results. * Other. Other types of research can include, for example, reviews, opinion papers, etc. It is also possible to find some papers that can be classified into different categories, for example, an article can propose a new technique and perform an extensive experimental validation. * **MQ4**. Most of the research works are expected to have an empirical validation of the theoretical advances and proposals. These experimentation can be done in different ways. According to the authors of [89], the empirical research types can be classified into the following. * Case study. It is an empirical inquiry that investigates a phenomenon in its real-life context. One or many case studies can be described. * Survey. A survey is a method for collecting quantitative information related to aspects in RSA research, for example, through a questionnaire. * Experiment. This case refers to an empirical method applied under controlled conditions to observe its effects and the results of certain processes or treatments. Figure 1: PRISMA flow chart resulting in the present mapping study. Data-based experiments. This is a different case from the previous category, as the research does not involve new experiments, but the data available from previous experiments is used. It can be either a public or private database. Other. Other types can include meta-analysis, history-based evaluation, etc. It is also possible that some papers do not report any empirical validation. * **MQ5**. Another interesting aspect to analyze is the type of techniques that are used in the papers, that is, the computer vision or machine learning tasks that are addressed in [14]. Many different classifications can be found in the literature. Following the work in [82], in the present review, the techniques are classified as follows. * Image preprocessing and segmentation. Although they are different problems, the two are closely related since the input are images and the output are also images. Besides, they are typically the first steps of many computer vision systems. Image preprocessing includes the techniques whose purpose is to improve the quality of the images captured [90], e.g., to remove noise, enhance image contrast, correct geometric deformations, or remove artifacts.