【文章內(nèi)容簡介】 . Analysis of Variance Factorial Analysis of Variance (ANOVA) was performed in order to evaluate the effect of the type of sensor in the registered measurements, including T (by means of Sensirion and Intersema), RH, barometric pressure, light intensity and acceleration module. ANOVA allows partitioning of the observed variance into ponents due to different explanatory variables. The STATISTICA software (StatSoft, Inc.) was used for this purpose [14]. The Fishers?s F ratio pares the variance within sample groups (“inherent variance”) with the variance between groups (factors). We use this statistic for knowing which factor has more influence in the variability of the measurements. . Psychrometric Data Psychrometry studies the thermodynamic properties of moist air and the use of these properties to analyze conditions and processes involving moist air. Psychrometric charts show a graphical representation of the relationship between T, RH and water vapor pressure in moist air. They can be used for the detection of water loss and condensation over the product. In our study, the ASAE standard was used for puting the psychrometric properties of air. Equations 2–5 and Table 1 enable the calculation of all psychrometric data of air whenever two independent psychrometric properties of an airwater vapour mixture are known in addition to the atmospheric pressure:where Ps stands for saturation vapor pressure (Pa), T is the temperature (K), Pv is the vapor pressure (Pa), H the absolute humidity (g/kg dry air), Patm is atmospheric pressure (Pa) and A, B, C, D, E, F, G and R are a series of coefficients used to pute Ps, according to Equation 3. 3. Results and Discussion . Reliability of Transmission Signal propagation through the lettuce lead to absorption of radio signals, resulting in great attenuations in RF signal strength and link quality at the receiver. During the experiment, only motes 3 and 4 were able to transmit to the coordinator. No signals were received from mote number 1, at the bottom of the first pallet, and number 2, in the middle of the pallet. Mote 3 was closer to the coordinator than mote 4, but mote 3 was surrounded by lettuce which blocks the RF signal. However between mote 4 and the coordinator there was free space for transmission. Thus, the maximum ratio of lost packets found was 100% for two of the motes and the minimum % 177。 %, for mote 4. Similar ratios were reported by several authors who performed experiments with WSN under real conditions, like for example in monitoring vineyards. Also, Baggio and Haneveld, after one year of experimentation in a potato field using motes operating at the band of 868/916MHz, reported that 98% of data packets were lost. However, during the second year the total amount of data gathered was 51%, which represents a clear improvement. Ipema et al. monitored cows with Crossbow motes, and found that the base station directly received less than 50% of temperature measurements stored in the mote buffer. Nadimi et al., who also monitored cows with this type of motes, showed packet loss rates of about 25% for wireless sensor data from cows in a pasture even the distance to the receiver (gateway) was less than m away. Radio propagation can be influenced by two main factors: the properties of propagation media and the heterogeneous properties of devices. In a mercial shipment, if the motes are embedded within the cargo, a significant portion of the Fresnel zone is obstructed. This is a big challenge in our application. Changing the motes? location, for example the one at the bottom of the pallets (mote 1, at the front of the semitrailer) or the one in the middle of the partment (mote 2), might have yielded in better data reception rates but would have resulted in a loss of spatial information near the floor or at midheight. The sensors should be as close as possible to the products transported。 otherwise the measurements would not give precise information. Thus, one solution, if the same motes are to be used, could be to include intermediates motes that allow peer to peer munication to the base station. Another solution could be to use lower frequencies。 however this is not possible using ZigBee, because the only radio frequency band available for ZigBee worldwide is the GHz one. The other ISM (Industrial, Scientific and Medical) bands (868 MHz and 915 MHz) differ from USA to Europe. Other options include developing motes with more RF power that can achieve longer radio ranges. The transmission could also be improved by optimizing antenna orientation, shape and configuration. The standard antenna mounted in the Micaz is a 3 cm long 1/2 wavelength dipole antenna. The munications could be enhanced using ceramic collinear antennas or with use of a simple reflecting screen to supplement a primary antenna,