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Chapter 8 A review on plant diseases recognition through deep learning 233

5. Remote sensing of plant diseases

Remote sensing is an advanced technology for gathering informa-
tion remotely by measuring the electromagnetic energy emitted
by the surface [29]. These measurements are analyzed to gather
the information regarding the object. Remote sensing is an indi-
rect assessment method and remotely monitors the vegetation
process to assess the plant health and pattern of vegetation. Lidar
and Radar are the remote sensing instruments.
Remote sensing assists in monitoring plant diseases, and it is
considered as a “radiodiagnosis” approach, which does contin-
uous monitoring of pests and diseases efficiently. Riley in 1989
stated the possible way to diagnose the damaged part occurred
due to pests and diseases by exploiting satellite or aerial images
[30]. Nilsson in the year 1995 demonstrated several applications
of image analysis and remote sensing in plant pathology [31]. In
recent years, feature extraction processes and algorithms are
examined in sensing systems, which reveals numerous possibil-
ities for remote monitoring of pests and diseases.

5.1 Detection of plant impairment using remote
sensing systems
Different pests and plant diseases would have various symptoms
and damages; remote sensing approaches are not appropriate for
all pests and plant diseases as they may lack in few identifiable
characteristics. Some root diseases and soil-based diseases could
cause systemic impacts on the functioning of plants that are
identifiable as well using sensing devices. However, identifying
and monitoring pests and plant diseases with remote sensing is
based on a certain response that is specifically detected by sensor
systems. Categories of impairment that occurred due to pests or
plant diseases and detected using remote sensing systems are as
follows:
1. Devastation of pigments: In certain cases, the pest attack and
disease infection cause devastation of chloroplast, which leads
to changes in pigment contents (anthocyanin, carotenoid, and
chlorophyll). Hyperspectral remote sensing observations are
generally required to identify this kind of response [32].
2. Pustules or lesions symptoms: The pustules or lesions are the
symptoms that occurred due to pests and diseases, which
too varies in shape and color among diseases. It can be
detected with the response of an abundance of pustules and
lesions [33,34].