Final answer:
Without the specified imagery sequence and data links, an accurate answer regarding the lowest water level of Lake Chad cannot be given. Lake Chad's water levels have fluctuated significantly over the years due to environmental and human factors.
Step-by-step explanation:
Based on the provided information about Lake Chad's water levels and the imagery from UNEP and NASA, the student is asked to identify when Lake Chad's water level was lowest. Unfortunately, without the specific imagery sequence or data links mentioned, it is not possible to provide an accurate response to this question. Nonetheless, Lake Chad is known for significant fluctuations in its water level over the past decades due to various factors including climate change, increased water usage, and irrigation practices. For an accurate answer, one would need to examine the specific satellite imagery data from the given years and compare the water levels documented during those times.