Mirage in desert occurs because of multiple times of refraction and total-reflection formed in the atmosphere.
Examples (Wiktionary)
Mandarin
你要知道，潜舰是看不见东西的。我在深海，水太深是看不见的，所以，只能靠声纳。声纳其实是一个很玄的东西，特别是在海里面的时候，因为有变温层，有温度的关系，有海水的密度的关系。你只要盐分的密度不同，海水的温度不同，那个声纳折射出来的东西基本上跟跋桮准不了多少，比跋桮略准一点。
你要知道，潛艦是看不見東西的。我在深海，水太深是看不見的，所以，只能靠聲納。聲納其實是一個很玄的東西，特別是在海里面的時候，因為有變温層，有温度的關係，有海水的密度的關係。你只要鹽分的密度不同，海水的温度不同，那個聲納折射出來的東西基本上跟跋桮準不了多少，比跋桮略準一點。
nǐ yào zhī dào ， qián jiàn shì kàn bù jiàn dōng xī de ． wǒ zài shēn hǎi ， shuǐ tài shēn shì kàn bù jiàn de ， suǒ yǐ ， zhǐ néng kào shēng nà ． shēng nà qí shí shì yī ge hěn xuán de dōng xī ， tè bié shì zài hǎi lǐ miàn de shí hòu ， yīn wèi yǒu biàn wēn céng ， yǒu wēn dù de guān xì ， yǒu hǎi shuǐ de mì dù de guān xì ． nǐ zhǐ yào yán fèn de mì dù bù tóng ， hǎi shuǐ de wēn dù bù tóng ， nà ge shēng nà zhé shè chū lái de dōng xī jī běn shàng gēn ｐｏａ̍ｈ po e zhǔn bù liao duō shǎo ， bǐ ｐｏａ̍ｈ po e lüè zhǔn yī diǎn ．
You have to understand, submarines are blind. When you enter the deep ocean, you can't see anything when the water is too deep and you must rely on sonar. Sonar is actually a very finicky thing, especially when used in the sea. This is because of the temperature change layer, which is connected to the temperature and oceanic water pressure. If the salt content density changes or if the ocean water temperature changes, the results of the sonar refraction will be essentially be little different from throwing poe, perhaps a tiny bit more useful than throwing poe.