Currently, there are significant challenges in the classification, recognition, and detection of fruits and vegetables. An important step to solve this problem is to obtain an accurate segmentation of the object of interest. However, the background and object separation in a gray image shows high errors for some thresholding techniques due to uneven or poorly conditioned lighting. An accepted strategy to decrease the error segmentation is to select the channel of a RGB image with high contrast. This paper presents the results of an experimental procedure based on a binary segmentation enhancement by using the Otsu method. The procedure was carried out with images of real agricultural products with and without additional noise to corroborate the robustness of the proposed strategy. The experimental tests were performed by using our database of RGB images of agricultural products under uncontrolled illumination. The results exhibit that the best segmentation is based on the selection of the Blue channel of the RGB test images due to its better contrast. Here, the quantitative results are measured by applying the Jaccard and Dice metrics based on the ground-truth images as optimal reference. Most of the results show an average percentage improvement difference greater than 45.5% in two experimental tests.

Object segmentation is a widely studied topic in digital image processing, as to it can be used for countless applications in several fields. This process is traditionally achieved by computing an optimal threshold from the image intensity histogram. Several algorithms have been proposed to find this threshold based on different statistical principles. However, the results generated via these algorithms contradict one another due to the many variables that can disturb an image. An accepted strategy to achieve the optimal histogram threshold, to distinguish between the object and the background, is to estimate two data distributions and find their intersection. This work proposes a strategy based on the Cuckoo Search Algorithm (CSA) and the Generalized Gaussian (GG) distribution to assess the optimal threshold. To test this methodology, we carried out several experiments in synthetic and practical scenarios and compared our results against other well-known algorithms from the literature. These practical cases comprise a medical image database and our own generated database. The results in a simulated environment show an evident advantage of the proposed strategy against other algorithms. In a real environment, this ranks among the best algorithms, making it a reliable alternative.

As in any satellite, onboard antennas for CubeSats are crucial to establish communication with ground stations or other satellites. According to its application, antennas must comply with standardized requirements related to size, bandwidth, operating frequency, polarization, and gain. This paper presents an ultrawideband circularly polarized two-layer crossed-dipole microstrip antenna for S-band CubeSat applications using genetic algorithms optimization tools included in the 3D electromagnetic simulation software Ansys HFSS. The antenna is constructed on a 10 × 10 cm Cuclad-250 substrate with a back copper flat plane, located at λ/4 at 2.25 GHz operating frequency. The backplane with the exact substrate dimensions improves gain and reduces inside satellite radiation. Measured bandwidth defined by S11 at a −10 dB was higher than 1835 MHz with S11 = −24.68 dB at the central frequency of 2.25 GHz, while measured VSWR at the same frequency was 1.124. At 2.25 GHz, the maximum measured gain and the minimum measured axial ratio in the broadside direction were found to be 6 dBi and 0.22 dB, respectively. There are antenna simulations and measurements, as long as its fabrication guarantees application requirements that make it ready for prespace testing.

A microstrip second-iteration square Koch dipole fractal antenna is presented. This meandered antenna has a total length of 56.56 cm including its feed gap and was printed on the diagonal of a 100 mm × 100 mm PCB card that acts as CubeSat face. The antenna that was designed to optimize space shows acceptable performance at its resonance frequency of 455 MHz within the 70-centimeter band, a band that is commonly used for TTC CubeSat subsystems. The designed fractal antenna shows a reflection coefficient below −20 dB, a VSWR below 1.2, a −10 dB bandwidth of 50 MHz, and impedance magnitude of 56 Ω, while the average maximum gain around its resonance frequency is 2.14 dBi. All these parameters make this designed antenna suitable for small satellite applications at a band where a linear λ/2 dipolar antenna working at 455 MHz would be about 32.97 cm long, which does not fit within the largest dimension of a CubeSat face corresponding to 14.14 cm.

In this article, the design and the integral implementation of a satellite ground station connected to the Internet of Things is presented. The communication system is based on long-range wireless technology, with the objective of receiving telemetry packets from a network of low-arth orbit satellites that transmit at frequencies around 433 MHz. The design covers mechanical design aspects, the control system, the antenna system, and the receiver. The ground station is oriented with respect to the elevation and azimuth coordinates obtained from a web page. This web page contains a console that shows the telemetry packets that have been received, as well as the satellite from which they came. The ground station is a low-cost proposal since commercial ground stations could be purchased at prices much higher than 2 orders of magnitude. All these aspects implied in this easy-to-replicate ground station are especially relevant in educational terms and for amateur radio enthusiasts.

Current small satellite platforms such as CubeSats require robust and versatile communication subsystems that allow the reconfiguration of the critical operating parameters such as carrier frequency, transmission power, bandwidth, or filter roll-off factor. A reconfigurable Analog Back-End for the space segment of a satellite communication subsystem is presented in this work. This prototype is implemented on a 9.5 cm² 6-layer PCB, and it operates from 0.070 to 6 GHz and complies with CubeSat and IPC-2221 standards. The processing, control, and synchronizing stages are carried out on a Software-Defined Radio approach executed on a baseband processor. Results showed that the signal power at the output of the proposed Analog Back-End is suitable for feeding the following antenna subsystem. Furthermore, the emitted radiation levels by the transmission lines do not generate electromagnetic interference.