United States citizens do not need a U.S. visa or passport for travel to Hawaii. If you are not a U.S. citizen, you may need a visa for entry into the US.
A citizen of a foreign country who seeks to enter the United States generally must first obtain a U.S. visa, which is placed in the traveler’s passport, a travel document issued by the traveler’s country of citizenship.
Certain international travelers may be eligible to travel to the United States without a visa if they meet the requirements for visa-free travel. The Visa section of this website is all about U.S. visas for foreign citizens to travel to the United States.
For more information about U.S. visa requirements please review the U.S. government website: https://travel.state.gov/content/travel/en/us-visas.html
As a general rule, passports must be valid for six months beyond the date the traveler will exit the U.S. Please check with the website, https://www.cbp.gov/, to confirm that your passport is compliant.
Passport Requirements article: https://help.cbp.gov/s/article/Article-905?language=en_US
A visa support letter can be provided for authors and registered attendees upon request.
There are 2 types of visa support letters available from IGARSS 2020: A Formal Acceptance Letter and an Official Registration Confirmation and Invitation.
This information is provided in good faith but travel regulations do change. The only authoritative sources of information are the U.S. Government website travel.state.gov/content/visas/en/visit.html